Method for decoding video for residual coding and device therefor

ABSTRACT

A method for decoding a video performed by a decoding device according to the present document is characterized by comprising: a step for acquiring video information including prediction mode information and residual information through a bitstream; a step for deriving a prediction mode of a current block on the basis of the prediction mode information; a step for deriving a prediction sample on the basis of the prediction mode; a step for deriving a current residual coefficient on the basis of residual syntax elements for the current residual coefficient in the current block; a step for deriving a residual sample on the basis of the current residual coefficient; and a step for deriving a reconstructed sample of the current block on the basis of the prediction sample and the residual sample.

BACKGROUND OF DISCLOSURE Field of the Disclosure

The present disclosure relates to image coding technology, and moreparticularly, to an image decoding method of coding simplified residualdata without performing level mapping in an image coding system, and anapparatus therefor.

Related Art

Recently, demand for high-resolution, high-quality images, such as HighDefinition (HD) images and Ultra High Definition (UHD) images, has beenincreasing in various fields. As the image data has high resolution andhigh quality, the amount of information or bits to be transmittedincreases relative to the legacy image data. Therefore, when image datais transmitted using a medium such as a conventional wired/wirelessbroadband line or image data is stored using an existing storage medium,the transmission cost and the storage cost thereof are increased.

Accordingly, there is a need for a highly efficient image compressiontechnique for effectively transmitting, storing, and reproducinginformation of high-resolution and high-quality images.

SUMMARY

The present disclosure provides a method and apparatus for improvingimage coding efficiency.

The present disclosure also provides a method and apparatus forimproving residual coding efficiency.

According to an embodiment of this document, an image decoding methodperformed by a decoding apparatus is provided. The method includesobtaining image information including residual information andprediction mode information through a bitstream, deriving a predictionmode of a current block based on the prediction mode information,deriving a prediction sample based on the prediction mode, deriving acurrent residual coefficient based on residual syntax elements for thecurrent residual coefficient in the current block, deriving a residualsample based on the current residual coefficient, and deriving areconstructed sample of the current block based on the residual sampleand the prediction sample.

According to another embodiment of this document, a decoding apparatusfor performing image decoding is provided. The decoding apparatusincludes an entropy decoder which obtains image information includingresidual information and prediction mode information through abitstream, a predictor which derives a prediction mode of a currentblock based on the prediction mode information, and derives a predictionsample based on the prediction mode, a residual processor which derivesa current residual coefficient based on residual syntax elements for thecurrent residual coefficient in the current block, and derives aresidual sample based on the current residual coefficient, and an adderwhich derives a reconstructed sample of the current block based on theresidual sample and the prediction sample.

According to still another embodiment of this document, a video encodingmethod which is performed by an encoding apparatus is provided. Themethod includes deriving a prediction sample of a current block based oninter prediction or intra prediction, deriving a residual sample of thecurrent block based on the prediction sample, deriving a currentresidual coefficient based on the residual sample, and encoding imageinformation including residual syntax elements for the current residualcoefficient and prediction mode information indicating a prediction modeof the current block.

According to still another embodiment of this document, a video encodingapparatus is provided. The encoding apparatus includes a predictor whichderives a prediction sample of a current block based on inter predictionor intra prediction, a residual processor which derives a residualsample of the current block based on the prediction sample, and derivesa current residual coefficient based on the residual sample, and anentropy encoder which encodes image information including residualsyntax elements for the current residual coefficient and prediction modeinformation indicating a prediction mode of the current block.

According to the present disclosure, it is possible to improve theefficiency of residual coding.

According to the present disclosure, it is possible to improve overallimage/video compression efficiency and reduce the coding complexity byderiving the residual coefficients to which the simplified residual datacoding is applied without performing level mapping.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 briefly illustrates an example of a video/image coding device towhich embodiments of the present disclosure are applicable.

FIG. 2 is a schematic diagram illustrating a configuration of avideo/image encoding apparatus to which the embodiment(s) of the presentdisclosure may be applied.

FIG. 3 is a schematic diagram illustrating a configuration of avideo/image decoding apparatus to which the embodiment(s) of the presentdisclosure may be applied.

FIG. 4 illustrates an example of an inter prediction-based video/imageencoding method.

FIG. 5 illustrates an example of an inter prediction-based video/imagedecoding method.

FIG. 6 schematically shows an inter prediction procedure.

FIG. 7 exemplarily shows context-adaptive binary arithmetic coding(CABAC) for encoding a syntax element.

FIG. 8 is a diagram showing exemplary transform coefficients within a4×4 block.

FIG. 9 illustrates an example of simplified residual data coding for oneCG, transform block, or coding block.

FIG. 10 illustrates another example of simplified residual data codingfor one CG, transform block, or coding block.

FIG. 11 illustrates another example of simplified residual data codingfor one CG, transform block, or coding block.

FIG. 12 briefly illustrates an image encoding method performed by anencoding apparatus according to the present disclosure.

FIG. 13 briefly illustrates an encoding apparatus for performing animage encoding method according to the present disclosure.

FIG. 14 briefly illustrates an image decoding method performed by adecoding apparatus according to the present disclosure.

FIG. 15 briefly illustrates a decoding apparatus for performing an imagedecoding method according to the present disclosure.

FIG. 16 illustrates a structural diagram of a contents streaming systemto which the present disclosure is applied.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The present disclosure may be modified in various forms, and specificembodiments thereof will be described and illustrated in the drawings.However, the embodiments are not intended for limiting the disclosure.The terms used in the following description are used to merely describespecific embodiments but are not intended to limit the disclosure. Anexpression of a singular number includes an expression of the pluralnumber, so long as it is clearly read differently. The terms such as“include” and “have” are intended to indicate that features, numbers,steps, operations, elements, components, or combinations thereof used inthe following description exist and it should be thus understood thatthe possibility of existence or addition of one or more differentfeatures, numbers, steps, operations, elements, components, orcombinations thereof is not excluded.

Meanwhile, elements in the drawings described in the disclosure areindependently drawn for the purpose of convenience for explanation ofdifferent specific functions, and do not mean that the elements areembodied by independent hardware or independent software. For example,two or more elements of the elements may be combined to form a singleelement, or one element may be partitioned into plural elements. Theembodiments in which the elements are combined and/or partitioned belongto the disclosure without departing from the concept of the disclosure.

Hereinafter, embodiments of the present disclosure will be described indetail with reference to the accompanying drawings. In addition, likereference numerals are used to indicate like elements throughout thedrawings, and the same descriptions on the like elements will beomitted.

FIG. 1 briefly illustrates an example of a video/image coding device towhich embodiments of the present disclosure are applicable.

Referring to FIG. 1, a video/image coding system may include a firstdevice (source device) and a second device (receiving device). Thesource device may deliver encoded video/image information or data in theform of a file or streaming to the receiving device via a digitalstorage medium or network.

The source device may include a video source, an encoding apparatus, anda transmitter. The receiving device may include a receiver, a decodingapparatus, and a renderer. The encoding apparatus may be called avideo/image encoding apparatus, and the decoding apparatus may be calleda video/image decoding apparatus. The transmitter may be included in theencoding apparatus. The receiver may be included in the decodingapparatus. The renderer may include a display, and the display may beconfigured as a separate device or an external component.

The video source may acquire video/image through a process of capturing,synthesizing, or generating the video/image. The video source mayinclude a video/image capture device and/or a video/image generatingdevice. The video/image capture device may include, for example, one ormore cameras, video/image archives including previously capturedvideo/images, and the like. The video/image generating device mayinclude, for example, computers, tablets and smartphones, and may(electronically) generate video/images. For example, a virtualvideo/image may be generated through a computer or the like. In thiscase, the video/image capturing process may be replaced by a process ofgenerating related data.

The encoding apparatus may encode input image/image. The encodingapparatus may perform a series of procedures such as prediction,transform, and quantization for compression and coding efficiency. Theencoded data (encoded video/image information) may be output in the formof a bit stream.

The transmitter may transmit the encoded image/image information or dataoutput in the form of a bit stream to the receiver of the receivingdevice through a digital storage medium or a network in the form of afile or streaming. The digital storage medium may include variousstorage mediums such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, and thelike. The transmitter may include an element for generating a media filethrough a predetermined file format and may include an element fortransmission through a broadcast/communication network. The receiver mayreceive/extract the bit stream and transmit the received bit stream tothe decoding apparatus.

The decoding apparatus may decode the video/image by performing a seriesof procedures such as dequantization, inverse transform, and predictioncorresponding to the operation of the encoding apparatus.

The renderer may render the decoded video/image. The renderedvideo/image may be displayed through the display.

Present disclosure relates to video/image coding. For example, themethods/embodiments disclosed in the present disclosure may be appliedto a method disclosed in the versatile video coding (VVC), the EVC(essential video coding) standard, the AOMedia Video 1 (AV1) standard,the 2nd generation of audio video coding standard (AVS2), or the nextgeneration video/image coding standard (e.g., H.267 or H.268, etc.).

Present disclosure presents various embodiments of video/image coding,and the embodiments may be performed in combination with each otherunless otherwise mentioned.

In the present disclosure, video may refer to a series of images overtime. Picture generally refers to a unit representing one image in aspecific time zone, and a subpicture/slice/tile is a unit constitutingpart of a picture in coding. The subpicture/slice/tile may include oneor more coding tree units (CTUs). One picture may consist of one or moresubpictures/slices/tiles. One picture may consist of one or more tilegroups. One tile group may include one or more tiles. A brick mayrepresent a rectangular region of CTU rows within a tile in a picture. Atile may be partitioned into multiple bricks, each of which consistingof one or more CTU rows within the tile. A tile that is not partitionedinto multiple bricks may be also referred to as a brick. A brick scan isa specific sequential ordering of CTUs partitioning a picture in whichthe CTUs are ordered consecutively in CTU raster scan in a brick, brickswithin a tile are ordered consecutively in a raster scan of the bricksof the tile, and tiles in a picture are ordered consecutively in araster scan of the tiles of the picture. In addition, a subpicture mayrepresent a rectangular region of one or more slices within a picture.That is, a subpicture contains one or more slices that collectivelycover a rectangular region of a picture. A tile is a rectangular regionof CTUs within a particular tile column and a particular tile row in apicture. The tile column is a rectangular region of CTUs having a heightequal to the height of the picture and a width specified by syntaxelements in the picture parameter set. The tile row is a rectangularregion of CTUs having a height specified by syntax elements in thepicture parameter set and a width equal to the width of the picture. Atile scan is a specific sequential ordering of CTUs partitioning apicture in which the CTUs are ordered consecutively in CTU raster scanin a tile whereas tiles in a picture are ordered consecutively in araster scan of the tiles of the picture. A slice includes an integernumber of bricks of a picture that may be exclusively contained in asingle NAL unit. A slice may consist of either a number of completetiles or only a consecutive sequence of complete bricks of one tile.Tile groups and slices may be used interchangeably in the presentdisclosure. For example, in the present disclosure, a tile group/tilegroup header may be called a slice/slice header.

A pixel or a pel may mean a smallest unit constituting one picture (orimage). Also, ‘sample’ may be used as a term corresponding to a pixel. Asample may generally represent a pixel or a value of a pixel, and mayrepresent only a pixel/pixel value of a luma component or only apixel/pixel value of a chroma component.

A unit may represent a basic unit of image processing. The unit mayinclude at least one of a specific region of the picture and informationrelated to the region. One unit may include one luma block and twochroma (e.g., cb, cr) blocks. The unit may be used interchangeably withterms such as block or area in some cases. In a general case, an M×Nblock may include samples (or sample arrays) or a set (or array) oftransform coefficients of M columns and N rows.

In the present description, “A or B” may mean “only A”, “only B” or“both A and B”. In other words, in the present specification, “A or B”may be interpreted as “A and/or B”. For example, “A, B or C” hereinmeans “only A”, “only B”, “only C”, or “any and any combination of A, Band C”.

A slash (/) or a comma (comma) used in the present description may mean“and/or”. For example, “A/B” may mean “A and/or B”. Accordingly, “A/B”may mean “only A”, “only B”, or “both A and B”. For example, “A, B, C”may mean “A, B, or C”.

In the present description, “at least one of A and B” may mean “only A”,“only B”, or “both A and B”. In addition, in the present description,the expression “at least one of A or B” or “at least one of A and/or B”may be interpreted the same as “at least one of A and B”.

In addition, in the present description, “at least one of A, B and C”means “only A”, “only B”, “only C”, or “any combination of A, B and C”.Also, “at least one of A, B or C” or “at least one of A, B and/or C” maymean “at least one of A, B and C”.

In addition, parentheses used in the present description may mean “forexample”. Specifically, when “prediction (intra prediction)” isindicated, “intra prediction” may be proposed as an example of“prediction”. In other words, “prediction” in the present description isnot limited to “intra prediction”, and “intra prediction” may beproposed as an example of “prediction”. Also, even when “prediction(i.e., intra prediction)” is indicated, “intra prediction” may beproposed as an example of “prediction”.

In the present description, technical features that are individuallydescribed within one drawing may be implemented individually or may beimplemented at the same time.

The following drawings were created to explain a specific example of thepresent description. Since the names of specific devices described inthe drawings or the names of specific signals/messages/fields arepresented by way of example, the technical features of the presentdescription are not limited to the specific names used in the followingdrawings.

FIG. 2 is a schematic diagram illustrating a configuration of avideo/image encoding apparatus to which the embodiment(s) of the presentdisclosure may be applied. Hereinafter, the video encoding apparatus mayinclude an image encoding apparatus.

Referring to FIG. 2, the encoding apparatus 200 includes an imagepartitioner 210, a predictor 220, a residual processor 230, and anentropy encoder 240, an adder 250, a filter 260, and a memory 270. Thepredictor 220 may include an inter predictor 221 and an intra predictor222. The residual processor 230 may include a transformer 232, aquantizer 233, a dequantizer 234, and an inverse transformer 235. Theresidual processor 230 may further include a subtractor 231. The adder250 may be called a reconstructor or a reconstructed block generator.The image partitioner 210, the predictor 220, the residual processor230, the entropy encoder 240, the adder 250, and the filter 260 may beconfigured by at least one hardware component (e.g., an encoder chipsetor processor) according to an embodiment. In addition, the memory 270may include a decoded picture buffer (DPB) or may be configured by adigital storage medium. The hardware component may further include thememory 270 as an internal/external component.

The image partitioner 210 may partition an input image (or a picture ora frame) input to the encoding apparatus 200 into one or moreprocessors. For example, the processor may be called a coding unit (CU).In this case, the coding unit may be recursively partitioned accordingto a quad-tree binary-tree ternary-tree (QTBTTT) structure from a codingtree unit (CTU) or a largest coding unit (LCU). For example, one codingunit may be partitioned into a plurality of coding units of a deeperdepth based on a quad tree structure, a binary tree structure, and/or aternary structure. In this case, for example, the quad tree structuremay be applied first and the binary tree structure and/or ternarystructure may be applied later. Alternatively, the binary tree structuremay be applied first. The coding procedure according to the presentdisclosure may be performed based on the final coding unit that is nolonger partitioned. In this case, the largest coding unit may be used asthe final coding unit based on coding efficiency according to imagecharacteristics, or if necessary, the coding unit may be recursivelypartitioned into coding units of deeper depth and a coding unit havingan optimal size may be used as the final coding unit. Here, the codingprocedure may include a procedure of prediction, transform, andreconstruction, which will be described later. As another example, theprocessor may further include a prediction unit (PU) or a transform unit(TU). In this case, the prediction unit and the transform unit may besplit or partitioned from the aforementioned final coding unit. Theprediction unit may be a unit of sample prediction, and the transformunit may be a unit for deriving a transform coefficient and/or a unitfor deriving a residual signal from the transform coefficient.

The unit may be used interchangeably with terms such as block or area insome cases. In a general case, an M×N block may represent a set ofsamples or transform coefficients composed of M columns and N rows. Asample may generally represent a pixel or a value of a pixel, mayrepresent only a pixel/pixel value of a luma component or represent onlya pixel/pixel value of a chroma component. A sample may be used as aterm corresponding to one picture (or image) for a pixel or a pel.

In the encoding apparatus 200, a prediction signal (predicted block,prediction sample array) output from the inter predictor 221 or theintra predictor 222 is subtracted from an input image signal (originalblock, original sample array) to generate a residual signal residualblock, residual sample array), and the generated residual signal istransmitted to the transformer 232. In this case, as shown, a unit forsubtracting a prediction signal (predicted block, prediction samplearray) from the input image signal (original block, original samplearray) in the encoder 200 may be called a subtractor 231. The predictormay perform prediction on a block to be processed (hereinafter, referredto as a current block) and generate a predicted block includingprediction samples for the current block. The predictor may determinewhether intra prediction or inter prediction is applied on a currentblock or CU basis. As described later in the description of eachprediction mode, the predictor may generate various information relatedto prediction, such as prediction mode information, and transmit thegenerated information to the entropy encoder 240. The information on theprediction may be encoded in the entropy encoder 240 and output in theform of a bit stream.

The intra predictor 222 may predict the current block by referring tothe samples in the current picture. The referred samples may be locatedin the neighborhood of the current block or may be located apartaccording to the prediction mode. In the intra prediction, predictionmodes may include a plurality of non-directional modes and a pluralityof directional modes. The non-directional mode may include, for example,a DC mode and a planar mode. The directional mode may include, forexample, 33 directional prediction modes or 65 directional predictionmodes according to the degree of detail of the prediction direction.However, this is merely an example, more or less directional predictionmodes may be used depending on a setting. The intra predictor 222 maydetermine the prediction mode applied to the current block by using aprediction mode applied to a neighboring block.

The inter predictor 221 may derive a predicted block for the currentblock based on a reference block (reference sample array) specified by amotion vector on a reference picture. Here, in order to reduce theamount of motion information transmitted in the inter prediction mode,the motion information may be predicted in units of blocks, sub-blocks,or samples based on correlation of motion information between theneighboring block and the current block. The motion information mayinclude a motion vector and a reference picture index. The motioninformation may further include inter prediction direction (L0prediction, L1 prediction, Bi prediction, etc.) information. In the caseof inter prediction, the neighboring block may include a spatialneighboring block present in the current picture and a temporalneighboring block present in the reference picture. The referencepicture including the reference block and the reference pictureincluding the temporal neighboring block may be the same or different.The temporal neighboring block may be called a collocated referenceblock, a co-located CU (colCU), and the like, and the reference pictureincluding the temporal neighboring block may be called a collocatedpicture (colPic). For example, the inter predictor 221 may configure amotion information candidate list based on neighboring blocks andgenerate information indicating which candidate is used to derive amotion vector and/or a reference picture index of the current block.Inter prediction may be performed based on various prediction modes. Forexample, in the case of a skip mode and a merge mode, the interpredictor 221 may use motion information of the neighboring block asmotion information of the current block. In the skip mode, unlike themerge mode, the residual signal may not be transmitted. In the case ofthe motion vector prediction (MVP) mode, the motion vector of theneighboring block may be used as a motion vector predictor and themotion vector of the current block may be indicated by signaling amotion vector difference.

The predictor 220 may generate a prediction signal based on variousprediction methods described below. For example, the predictor may notonly apply intra prediction or inter prediction to predict one block butalso simultaneously apply both intra prediction and inter prediction.This may be called combined inter and intra prediction (CIIP). Inaddition, the predictor may be based on an intra block copy (IBC)prediction mode or a palette mode for prediction of a block. The IBCprediction mode or palette mode may be used for content image/videocoding of a game or the like, for example, screen content coding (SCC).The IBC basically performs prediction in the current picture but may beperformed similarly to inter prediction in that a reference block isderived in the current picture. That is, the IBC may use at least one ofthe inter prediction techniques described in the present disclosure. Thepalette mode may be considered as an example of intra coding or intraprediction. When the palette mode is applied, a sample value within apicture may be signaled based on information on the palette table andthe palette index.

The prediction signal generated by the predictor (including the interpredictor 221 and/or the intra predictor 222) may be used to generate areconstructed signal or to generate a residual signal. The transformer232 may generate transform coefficients by applying a transformtechnique to the residual signal. For example, the transform techniquemay include at least one of a discrete cosine transform (DCT), adiscrete sine transform (DST), a Karhunen-loéve transform (KLT), agraph-based transform (GBT), or a conditionally non-linear transform(CNT). Here, the GBT means transform obtained from a graph whenrelationship information between pixels is represented by the graph. TheCNT refers to transform generated based on a prediction signal generatedusing all previously reconstructed pixels. In addition, the transformprocess may be applied to square pixel blocks having the same size ormay be applied to blocks having a variable size rather than square.

The quantizer 233 may quantize the transform coefficients and transmitthem to the entropy encoder 240 and the entropy encoder 240 may encodethe quantized signal (information on the quantized transformcoefficients) and output a bit stream. The information on the quantizedtransform coefficients may be referred to as residual information. Thequantizer 233 may rearrange block type quantized transform coefficientsinto a one-dimensional vector form based on a coefficient scanning orderand generate information on the quantized transform coefficients basedon the quantized transform coefficients in the one-dimensional vectorform. Information on transform coefficients may be generated. Theentropy encoder 240 may perform various encoding methods such as, forexample, exponential Golomb, context-adaptive variable length coding(CAVLC), context-adaptive binary arithmetic coding (CABAC), and thelike. The entropy encoder 240 may encode information necessary forvideo/image reconstruction other than quantized transform coefficients(e.g., values of syntax elements, etc.) together or separately. Encodedinformation (e.g., encoded video/image information) may be transmittedor stored in units of NALs (network abstraction layer) in the form of abit stream. The video/image information may further include informationon various parameter sets such as an adaptation parameter set (APS), apicture parameter set (PPS), a sequence parameter set (SPS), or a videoparameter set (VPS). In addition, the video/image information mayfurther include general constraint information. In the presentdisclosure, information and/or syntax elements transmitted/signaled fromthe encoding apparatus to the decoding apparatus may be included invideo/picture information. The video/image information may be encodedthrough the above-described encoding procedure and included in the bitstream. The bit stream may be transmitted over a network or may bestored in a digital storage medium. The network may include abroadcasting network and/or a communication network, and the digitalstorage medium may include various storage media such as USB, SD, CD,DVD, Blu-ray, HDD, SSD, and the like. A transmitter (not shown)transmitting a signal output from the entropy encoder 240 and/or astorage unit (not shown) storing the signal may be included asinternal/external element of the encoding apparatus 200, andalternatively, the transmitter may be included in the entropy encoder240.

The quantized transform coefficients output from the quantizer 233 maybe used to generate a prediction signal. For example, the residualsignal (residual block or residual samples) may be reconstructed byapplying dequantization and inverse transform to the quantized transformcoefficients through the dequantizer 234 and the inverse transformer235. The adder 250 adds the reconstructed residual signal to theprediction signal output from the inter predictor 221 or the intrapredictor 222 to generate a reconstructed signal (reconstructed picture,reconstructed block, reconstructed sample array). If there is noresidual for the block to be processed, such as a case where the skipmode is applied, the predicted block may be used as the reconstructedblock. The adder 250 may be called a reconstructor or a reconstructedblock generator. The generated reconstructed signal may be used forintra prediction of a next block to be processed in the current pictureand may be used for inter prediction of a next picture through filteringas described below.

Meanwhile, luma mapping with chroma scaling (LMCS) may be applied duringpicture encoding and/or reconstruction.

The filter 260 may improve subjective/objective image quality byapplying filtering to the reconstructed signal. For example, the filter260 may generate a modified reconstructed picture by applying variousfiltering methods to the reconstructed picture and store the modifiedreconstructed picture in the memory 270, specifically, a DPB of thememory 270. The various filtering methods may include, for example,deblocking filtering, a sample adaptive offset, an adaptive loop filter,a bilateral filter, and the like. The filter 260 may generate variousinformation related to the filtering and transmit the generatedinformation to the entropy encoder 240 as described later in thedescription of each filtering method. The information related to thefiltering may be encoded by the entropy encoder 240 and output in theform of a bit stream.

The modified reconstructed picture transmitted to the memory 270 may beused as the reference picture in the inter predictor 221. When the interprediction is applied through the encoding apparatus, predictionmismatch between the encoding apparatus 200 and the decoding apparatus300 may be avoided and encoding efficiency may be improved.

The DPB of the memory 270 DPB may store the modified reconstructedpicture for use as a reference picture in the inter predictor 221. Thememory 270 may store the motion information of the block from which themotion information in the current picture is derived (or encoded) and/orthe motion information of the blocks in the picture that have alreadybeen reconstructed. The stored motion information may be transmitted tothe inter predictor 221 and used as the motion information of thespatial neighboring block or the motion information of the temporalneighboring block. The memory 270 may store reconstructed samples ofreconstructed blocks in the current picture and may transfer thereconstructed samples to the intra predictor 222.

FIG. 3 is a schematic diagram illustrating a configuration of avideo/image decoding apparatus to which the embodiment(s) of the presentdisclosure may be applied.

Referring to FIG. 3, the decoding apparatus 300 may include an entropydecoder 310, a residual processor 320, a predictor 330, an adder 340, afilter 350, and a memory 360. The predictor 330 may include an interpredictor 331 and an intra predictor 332. The residual processor 320 mayinclude a dequantizer 321 and an inverse transformer 322. The entropydecoder 310, the residual processor 320, the predictor 330, the adder340, and the filter 350 may be configured by a hardware component (e.g.,a decoder chipset or a processor) according to an embodiment. Inaddition, the memory 360 may include a decoded picture buffer (DPB) ormay be configured by a digital storage medium. The hardware componentmay further include the memory 360 as an internal/external component.

When a bit stream including video/image information is input, thedecoding apparatus 300 may reconstruct an image corresponding to aprocess in which the video/image information is processed in theencoding apparatus of FIG. 2. For example, the decoding apparatus 300may derive units/blocks based on block partition related informationobtained from the bit stream. The decoding apparatus 300 may performdecoding using a processor applied in the encoding apparatus. Thus, theprocessor of decoding may be a coding unit, for example, and the codingunit may be partitioned according to a quad tree structure, binary treestructure and/or ternary tree structure from the coding tree unit or thelargest coding unit. One or more transform units may be derived from thecoding unit. The reconstructed image signal decoded and output throughthe decoding apparatus 300 may be reproduced through a reproducingapparatus.

The decoding apparatus 300 may receive a signal output from the encodingapparatus of FIG. 2 in the form of a bit stream, and the received signalmay be decoded through the entropy decoder 310. For example, the entropydecoder 310 may parse the bit stream to derive information (e.g.,video/image information) necessary for image reconstruction (or picturereconstruction). The video/image information may further includeinformation on various parameter sets such as an adaptation parameterset (APS), a picture parameter set (PPS), a sequence parameter set(SPS), or a video parameter set (VPS). In addition, the video/imageinformation may further include general constraint information. Thedecoding apparatus may further decode picture based on the informationon the parameter set and/or the general constraint information.Signaled/received information and/or syntax elements described later inthe present disclosure may be decoded may decode the decoding procedureand obtained from the bit stream. For example, the entropy decoder 310decodes the information in the bit stream based on a coding method suchas exponential Golomb coding, CAVLC, or CABAC, and output syntaxelements required for image reconstruction and quantized values oftransform coefficients for residual. More specifically, the CABACentropy decoding method may receive a bin corresponding to each syntaxelement in the bit stream, determine a context model using a decodingtarget syntax element information, decoding information of a decodingtarget block or information of a symbol/bin decoded in a previous stage,and perform an arithmetic decoding on the bin by predicting aprobability of occurrence of a bin according to the determined contextmodel, and generate a symbol corresponding to the value of each syntaxelement. In this case, the CABAC entropy decoding method may update thecontext model by using the information of the decoded symbol/bin for acontext model of a next symbol/bin after determining the context model.The information related to the prediction among the information decodedby the entropy decoder 310 may be provided to the predictor (the interpredictor 332 and the intra predictor 331), and the residual value onwhich the entropy decoding was performed in the entropy decoder 310,that is, the quantized transform coefficients and related parameterinformation, may be input to the residual processor 320. The residualprocessor 320 may derive the residual signal (the residual block, theresidual samples, the residual sample array). In addition, informationon filtering among information decoded by the entropy decoder 310 may beprovided to the filter 350. Meanwhile, a receiver (not shown) forreceiving a signal output from the encoding apparatus may be furtherconfigured as an internal/external element of the decoding apparatus300, or the receiver may be a component of the entropy decoder 310.Meanwhile, the decoding apparatus according to the present disclosuremay be referred to as a video/image/picture decoding apparatus, and thedecoding apparatus may be classified into an information decoder(video/image/picture information decoder) and a sample decoder(video/image/picture sample decoder). The information decoder mayinclude the entropy decoder 310, and the sample decoder may include atleast one of the dequantizer 321, the inverse transformer 322, the adder340, the filter 350, the memory 360, the inter predictor 332, and theintra predictor 331.

The dequantizer 321 may dequantize the quantized transform coefficientsand output the transform coefficients. The dequantizer 321 may rearrangethe quantized transform coefficients in the form of a two-dimensionalblock form. In this case, the rearrangement may be performed based onthe coefficient scanning order performed in the encoding apparatus. Thedequantizer 321 may perform dequantization on the quantized transformcoefficients by using a quantization parameter (e.g., quantization stepsize information) and obtain transform coefficients.

The inverse transformer 322 inversely transforms the transformcoefficients to obtain a residual signal (residual block, residualsample array).

The predictor may perform prediction on the current block and generate apredicted block including prediction samples for the current block. Thepredictor may determine whether intra prediction or inter prediction isapplied to the current block based on the information on the predictionoutput from the entropy decoder 310 and may determine a specificintra/inter prediction mode.

The predictor 320 may generate a prediction signal based on variousprediction methods described below. For example, the predictor may notonly apply intra prediction or inter prediction to predict one block butalso simultaneously apply intra prediction and inter prediction. Thismay be called combined inter and intra prediction (CIIP). In addition,the predictor may be based on an intra block copy (IBC) prediction modeor a palette mode for prediction of a block. The IBC prediction mode orpalette mode may be used for content image/video coding of a game or thelike, for example, screen content coding (SCC). The IBC basicallyperforms prediction in the current picture but may be performedsimilarly to inter prediction in that a reference block is derived inthe current picture. That is, the IBC may use at least one of the interprediction techniques described in the present disclosure. The palettemode may be considered as an example of intra coding or intraprediction. When the palette mode is applied, a sample value within apicture may be signaled based on information on the palette table andthe palette index.

The intra predictor 331 may predict the current block by referring tothe samples in the current picture. The referred samples may be locatedin the neighborhood of the current block or may be located apartaccording to the prediction mode. In the intra prediction, predictionmodes may include a plurality of non-directional modes and a pluralityof directional modes. The intra predictor 331 may determine theprediction mode applied to the current block by using a prediction modeapplied to a neighboring block.

The inter predictor 332 may derive a predicted block for the currentblock based on a reference block (reference sample array) specified by amotion vector on a reference picture. In this case, in order to reducethe amount of motion information transmitted in the inter predictionmode, motion information may be predicted in units of blocks,sub-blocks, or samples based on correlation of motion informationbetween the neighboring block and the current block. The motioninformation may include a motion vector and a reference picture index.The motion information may further include inter prediction direction(L0 prediction, L1 prediction, Bi prediction, etc.) information. In thecase of inter prediction, the neighboring block may include a spatialneighboring block present in the current picture and a temporalneighboring block present in the reference picture. For example, theinter predictor 332 may configure a motion information candidate listbased on neighboring blocks and derive a motion vector of the currentblock and/or a reference picture index based on the received candidateselection information. Inter prediction may be performed based onvarious prediction modes, and the information on the prediction mayinclude information indicating a mode of inter prediction for thecurrent block.

The adder 340 may generate a reconstructed signal (reconstructedpicture, reconstructed block, reconstructed sample array) by adding theobtained residual signal to the prediction signal (predicted block,predicted sample array) output from the predictor (including the interpredictor 332 and/or the intra predictor 331). If there is no residualfor the block to be processed, such as when the skip mode is applied,the predicted block may be used as the reconstructed block.

The adder 340 may be called reconstructor or a reconstructed blockgenerator. The generated reconstructed signal may be used for intraprediction of a next block to be processed in the current picture, maybe output through filtering as described below, or may be used for interprediction of a next picture.

Meanwhile, luma mapping with chroma scaling (LMCS) may be applied in thepicture decoding process.

The filter 350 may improve subjective/objective image quality byapplying filtering to the reconstructed signal. For example, the filter350 may generate a modified reconstructed picture by applying variousfiltering methods to the reconstructed picture and store the modifiedreconstructed picture in the memory 360, specifically, a DPB of thememory 360. The various filtering methods may include, for example,deblocking filtering, a sample adaptive offset, an adaptive loop filter,a bilateral filter, and the like.

The (modified) reconstructed picture stored in the DPB of the memory 360may be used as a reference picture in the inter predictor 332. Thememory 360 may store the motion information of the block from which themotion information in the current picture is derived (or decoded) and/orthe motion information of the blocks in the picture that have alreadybeen reconstructed. The stored motion information may be transmitted tothe inter predictor 260 so as to be utilized as the motion informationof the spatial neighboring block or the motion information of thetemporal neighboring block. The memory 360 may store reconstructedsamples of reconstructed blocks in the current picture and transfer thereconstructed samples to the intra predictor 331.

In the present disclosure, the embodiments described in the filter 260,the inter predictor 221, and the intra predictor 222 of the encodingapparatus 200 may be the same as or respectively applied to correspondto the filter 350, the inter predictor 332, and the intra predictor 331of the decoding apparatus 300. The same may also apply to the unit 332and the intra predictor 331.

In the present disclosure, at least one of quantization/inversequantization and/or transform/inverse transform may be omitted. When thequantization/inverse quantization is omitted, the quantized transformcoefficients may be called transform coefficients. When thetransform/inverse transform is omitted, the transform coefficients maybe called coefficients or residual coefficients, or may still be calledtransform coefficients for uniformity of expression.

In the present disclosure, a quantized transform coefficient and atransform coefficient may be referred to as a transform coefficient anda scaled transform coefficient, respectively. In this case, the residualinformation may include information on transform coefficient(s), and theinformation on the transform coefficient(s) may be signaled throughresidual coding syntax. Transform coefficients may be derived based onthe residual information (or the information on the transformcoefficient(s)), and scaled transform coefficients may be derived byinverse transforming (scaling) on the transform coefficients. Residualsamples may be derived based on the inverse transforming (transforming)on the scaled transform coefficients. This may be applied/expressed inother parts of the present disclosure as well.

As described above, in performing video coding, prediction is performedto improve compression efficiency. Through this, a predicted blockincluding prediction samples for a current block as a block to be coded(i.e., a coding target block) may be generated. Here, the predictedblock includes prediction samples in a spatial domain (or pixel domain).The predicted block is derived in the same manner in an encodingapparatus and a decoding apparatus, and the encoding apparatus maysignal information (residual information) on residual between theoriginal block and the predicted block, rather than an original samplevalue of an original block, to the decoding apparatus, therebyincreasing image coding efficiency. The decoding apparatus may derive aresidual block including residual samples based on the residualinformation, add the residual block and the predicted block to generatereconstructed blocks including reconstructed samples, and generate areconstructed picture including the reconstructed blocks.

The residual information may be generated through a transform andquantization procedure. For example, the encoding apparatus may derive aresidual block between the original block and the predicted block,perform a transform procedure on residual samples (residual samplearray) included in the residual block to derive transform coefficients,perform a quantization procedure on the transform coefficients to derivequantized transform coefficients, and signal related residualinformation to the decoding apparatus (through a bit stream). Here, theresidual information may include value information of the quantizedtransform coefficients, location information, a transform technique, atransform kernel, a quantization parameter, and the like. The decodingapparatus may perform dequantization/inverse transform procedure basedon the residual information and derive residual samples (or residualblocks). The decoding apparatus may generate a reconstructed picturebased on the predicted block and the residual block. Also, for referencefor inter prediction of a picture afterward, the encoding apparatus mayalso dequantize/inverse-transform the quantized transform coefficientsto derive a residual block and generate a reconstructed picture basedthereon.

Intra prediction may refer to prediction that generates predictionsamples for a current block based on reference samples in a picture towhich the current block belongs (hereinafter, referred to as a currentpicture). When the intra prediction is applied to the current block,neighboring reference samples to be used for the intra prediction of thecurrent block may be derived. The neighboring reference samples of thecurrent block may include a sample adjacent to the left boundary of thecurrent block of size nW×nH and a total of 2×nH samples adjacent to thebottom-left of the current block, a sample adjacent to the top boundaryof the current block and a total of 2×nW samples adjacent to thetop-right and a sample adjacent to the top-left of the current block.Alternatively, the neighboring reference samples of the current blockmay include a plurality of columns of top neighboring samples and aplurality of rows of left neighboring samples. In addition, theneighboring reference samples of the current block may include a totalof nH samples adjacent to the right boundary of the current block ofsize nW×nH, a total of nW samples adjacent to the bottom boundary of thecurrent block and a sample adjacent to the bottom-right of the currentblock.

However, some of the neighboring reference samples of the current blockhave not yet been decoded or may not be available. In this case, thedecoder may construct neighboring reference samples to be used forprediction by substituting unavailable samples with available samples.Alternatively, neighboring reference samples to be used for predictionmay be configured through interpolation of available samples.

When the neighboring reference samples are derived, (i) a predictionsample may be derived based on the average or interpolation ofneighboring reference samples of the current block, or (ii) theprediction sample may be derived based on a reference sample existing ina specific (prediction) direction with respect to a prediction sampleamong the neighboring reference samples of the current block. The caseof (i) may be called a non-directional mode or a non-angular mode, andthe case of (ii) may be called a directional mode or an angular mode.

In addition, the prediction sample may be generated throughinterpolation of a first neighboring sample located in the predictiondirection of the intra prediction mode of the current block based on theprediction sample of the current block and a second neighboring samplelocated in a direction opposite to the prediction direction among theneighboring reference samples. The above-described case may be referredto as linear interpolation intra prediction (LIP). In addition, chromaprediction samples may be generated based on the luma samples using alinear model (LM). This case may be called an LM mode or a chromacomponent LM (CCLM) mode.

In addition, a temporary prediction sample of the current block isderived based on the filtered neighboring reference samples, and aprediction sample of the current block may also be derived by weightedsumming the temporary prediction sample and at least one referencesample derived according to the intra prediction mode among the existingneighboring reference samples, that is, unfiltered neighboring referencesamples. The above-described case may be referred to as positiondependent intra prediction (PDPC).

In addition, a reference sample line with the highest predictionaccuracy among neighboring multiple reference sample lines of thecurrent block is selected, and a prediction sample is derived using areference sample located in the prediction direction in the selectedline. In this case, intra prediction encoding may be performed byindicating (signaling) the used reference sample line to the decodingapparatus. The above-described case may be referred to asmulti-reference line intra prediction or MRL-based intra prediction.

In addition, the current block is divided into vertical or horizontalsub-partitions and intra prediction is performed based on the same intraprediction mode, but neighboring reference samples may be derived andused in units of the sub-partitions. That is, in this case, the intraprediction mode for the current block is equally applied to thesub-partitions, but the intra prediction performance may be improved insome cases by deriving and using the neighboring reference samples inunits of the sub-partitions. This prediction method may be calledintra-prediction based on intra sub-partitions (ISP).

The above-described intra prediction methods may be called intraprediction types to be distinguished from the intra prediction mode. Theintra prediction types may be referred to by various terms such as intraprediction technique or additional intra prediction modes. For example,the intra prediction types (or additional intra prediction modes, etc.)may include at least one of the aforementioned LIP, PDPC, MRL, and ISP.A general intra prediction method excluding a specific intra predictiontype such as LIP, PDPC, MRL, and ISP may be referred to as a normalintra prediction type. The normal intra prediction type may be generallyapplied when the above specific intra prediction type is not applied,and prediction may be performed based on the above-described intraprediction mode. Meanwhile, if necessary, post-processing filtering maybe performed on the derived prediction sample.

Specifically, the intra prediction process may include an intraprediction mode/type determination step, neighboring reference samplesderivation step, and an intra prediction mode/type based predictionsample derivation step. In addition, if necessary, a post-filtering stepmay be performed on the derived prediction sample.

When intra prediction is applied, an intra prediction mode applied tothe current block may be determined using an intra prediction mode of aneighboring block. For example, the decoding device may select one ofmost probable mode (MPM) candidates in the MPM list derived based onadditional candidate modes and an intra prediction mode of theneighboring block (e.g., the left and/or top neighboring block) of thecurrent block, or select one of the remaining intra prediction modes notincluded in the MPM candidates (and planar mode) based on the remainingintra prediction mode information. The MPM list may be configured toinclude or not include the planner mode as a candidate. For example,when the MPM list includes a planner mode as a candidate, the MPM listmay have 6 candidates, and when the MPM list does not include a plannermode as a candidate, the MPM list may have 5 candidates. When the MPMlist does not include the planar mode as a candidate, a not planar flag(e.g., intra_luma_not_planar_flag) representing whether the intraprediction mode of the current block is not the planar mode may besignaled. For example, the MPM flag may be signaled first, and the MPMindex and not planner flag may be signaled when the value of the MPMflag is 1. Also, the MPM index may be signaled when the value of the notplanner flag is 1. Here, the fact that the MPM list is configured not toinclude the planner mode as a candidate is that the planner mode isalways considered as MPM rather than that the planner mode is not MPM,thus, the flag (not planar flag) is signaled first to check whether itis the planar mode.

For example, whether the intra prediction mode applied to the currentblock is among the MPM candidates (and the planar mode) or the remainingmodes may be indicated based on the MPM flag (e.g.,intra_luma_mpm_flag). The MPM flag with a value of 1 may indicate thatthe intra prediction mode for the current block is within MPM candidates(and planar mode), and The MPM flag with a value of 0 may indicate thatthe intra prediction mode for the current block is not within MPMcandidates (and planar mode). The not planar flag (e.g.,intra_luma_not_planar_flag) with a value of 0 may indicate that theintra prediction mode for the current block is a planar mode, and thenot planar flag with a value of 1 may indicate that the intra predictionmode for the current block is not the planar mode. The MPM index may besignaled in the form of an mpm_idx or intra_luma_mpm_idx syntax element,and the remaining intra prediction mode information may be signaled inthe form of a rem_intra_luma_pred_mode or intra_luma_mpm_remaindersyntax element. For example, the remaining intra prediction modeinformation may indicate one of the remaining intra prediction modes notincluded in the MPM candidates (and planar mode) among all intraprediction modes by indexing in the order of prediction mode number. Theintra prediction mode may be an intra prediction mode for a lumacomponent (sample). Hereinafter, the intra prediction mode informationmay include at least one of the MPM flag (e.g., intra_luma_mpm_flag),the not planar flag (e.g., intra_luma_not_planar_flag), the MPM index(e.g., mpm_idx or intra_luma_mpm_idx), or the remaining intra predictionmode information (rem_intra_luma_luma_mpm_mode or intra_luma_mpminder).In the present disclosure, the MPM list may be referred to by variousterms such as an MPM candidate list and candModeList. When the MIP isapplied to the current block, a separate MPM flag (e.g.,intra_mip_mpm_flag) for the MIP, an MPM index (e.g., intra_mip_mpm_idx),and remaining intra prediction mode information (e.g.,intra_mip_mpm_remainder) may be signaled, and the not planar flag maynot be signaled.

In other words, in general, when a block partition for an image isperformed, the current block to be coded and a neighboring block havesimilar image characteristics. Therefore, there is a high probabilitythat the current block and the neighboring block have the same orsimilar intra prediction mode. Accordingly, the encoder may use theintra prediction mode of the neighboring block to encode the intraprediction mode of the current block.

For example, the decoding device/encoding device may construct a mostprobable modes (MPM) list for the current block. The MPM list may bereferred to as the MPM candidate list. Here, the MPM may refer to modesused to improve coding efficiency in consideration of the similaritybetween the current block and the neighboring blocks during intraprediction mode coding. As described above, the MPM list may beconstructed to include the planar mode, or may be constructed to excludethe planar mode. For example, when the MPM list includes the planarmode, the number of candidates in the MPM list may be 6. And, when theMPM list does not include the planar mode, the number of candidates inthe MPM list may be 5.

The encoder/decoder may construct an MPM list including five or sixMPMs.

In order to construct the MPM list, three types of modes, such asdefault intra modes, neighbor intra modes, and derived intra modes, maybe considered.

For the neighbor intra modes, two neighbor blocks, that is, a leftneighbor block and a top neighbor block, may be considered.

As described above, if the MPM list is constructed to not include aplanar mode, the planar mode may be excluded from the list, and thenumber of MPM list candidates may be set to five.

Furthermore, anon-directional mode (or anon-angle mode) among the intraprediction modes may include a DC mode based on an average of neighborreference samples of a current block or an interpolation-based planarmode.

Meanwhile, when inter prediction is applied, the predictor of theencoding apparatus/decoding apparatus may derive prediction samples byperforming inter prediction in units of blocks. The inter prediction maybe applied when performing the prediction on the current block. That is,the predictor (more specifically, inter predictor) of theencoding/decoding apparatus may derive prediction samples by performingthe inter prediction in units of the block. The inter prediction mayrepresent prediction derived by a method dependent to the data elements(e.g., sample values or motion information) of a picture(s) other thanthe current picture. When the inter prediction is applied to the currentblock, a predicted block (prediction sample array) for the current blockmay be derived based on a reference block (reference sample array)specified by the motion vector on the reference picture indicated by thereference picture index. In this case, in order to reduce an amount ofmotion information transmitted in the inter-prediction mode, the motioninformation of the current block may be predicted in units of a block, asubblock, or a sample based on a correlation of the motion informationbetween the neighboring block and the current block. The motioninformation may include the motion vector and the reference pictureindex. The motion information may further include inter-prediction type(L0 prediction, L1 prediction, Bi prediction, etc.) information. In thecase of applying the inter prediction, the neighboring block may includea spatial neighboring block which is present in the current picture anda temporal neighboring block which is present in the reference picture.A reference picture including the reference block and a referencepicture including the temporal neighboring block may be the same as eachother or different from each other. The temporal neighboring block maybe referred to as a name such as a collocated reference block, acollocated CU (colCU), etc., and the reference picture including thetemporal neighboring block may be referred to as a collocated picture(colPic). For example, a motion information candidate list may beconfigured based on the neighboring blocks of the current block and aflag or index information indicating which candidate is selected (used)may be signaled in order to derive the motion vector and/or referencepicture index of the current block. The inter prediction may beperformed based on various prediction modes and for example, in the caseof a skip mode and a merge mode, the motion information of the currentblock may be the same as the motion information of the selectedneighboring block. In the case of the skip mode, the residual signal maynot be transmitted unlike the merge mode. In the case of a motion vectorprediction (MVP) mode, the motion vector of the selected neighboringblock may be used as a motion vector predictor and a motion vectordifference may be signaled. In this case, the motion vector of thecurrent block may be derived by using a sum of the motion vectorpredictor and the motion vector difference.

The motion information may further include L0 motion information and/orL1 motion information according to the inter-prediction type (L0prediction, L1 prediction, Bi prediction, etc.). A L0-direction motionvector may be referred to as an L0 motion vector or MVL0 and anL1-direction motion vector may be referred to as an L1 motion vector orMVL1. A prediction based on the L0 motion vector may be referred to asan L0 prediction, a prediction based on the L1 motion vector may bereferred to as an L1 prediction, and a prediction based on both the L0motion vector and the L1 motion vector may be referred to as abi-prediction. Here, the L0 motion vector may indicate a motion vectorassociated with a reference picture list L0 and the L1 motion vector mayindicate a motion vector associated with a reference picture list L1.The reference picture list L0 may include pictures prior to the currentpicture in an output order and the reference picture list L1 may includepictures subsequent to the current picture in the output order, as thereference pictures. The prior pictures may be referred to as a forward(reference) picture and the subsequent pictures may be referred to as areverse (reference) picture. The reference picture list L0 may furtherinclude the pictures subsequent to the current picture in the outputorder as the reference pictures. In this case, the prior pictures may befirst indexed in the reference picture list L0 and the subsequentpictures may then be indexed. The reference picture list L1 may furtherinclude the pictures prior to the current picture in the output order asthe reference pictures. In this case, the subsequent pictures may befirst indexed in the reference picture list L1 and the prior picturesmay then be indexed. Here, the output order may correspond to a pictureorder count (POC) order.

A video/image encoding process based on inter prediction mayschematically include, for example, the following.

FIG. 4 illustrates an example of an inter prediction-based video/imageencoding method.

The encoding apparatus performs the inter prediction for the currentblock (S400). The encoding apparatus may derive the inter predictionmode and the motion information of the current block and generate theprediction samples of the current block. Here, an inter prediction modedetermining process, a motion information deriving process, and ageneration process of the prediction samples may be simultaneouslyperformed and any one process may be performed earlier than otherprocess. For example, the inter-prediction unit of the encodingapparatus may include a prediction mode determination unit, a motioninformation derivation unit, and a prediction sample derivation unit,and the prediction mode determination unit may determine the predictionmode for the current block, the motion information derivation unit mayderive the motion information of the current block, and the predictionsample derivation unit may derive the prediction samples of the currentblock. For example, the inter-prediction unit of the encoding apparatusmay search a block similar to the current block in a predetermined area(search area) of reference pictures through motion estimation and derivea reference block in which a difference from the current block isminimum or is equal to or less than a predetermined criterion. Areference picture index indicating a reference picture at which thereference block is positioned may be derived based thereon and a motionvector may be derived based on a difference in location between thereference block and the current block. The encoding apparatus maydetermine a mode applied to the current block among various predictionmodes. The encoding apparatus may compare RD cost for the variousprediction modes and determine an optimal prediction mode for thecurrent block.

For example, when the skip mode or the merge mode is applied to thecurrent block, the encoding apparatus may configure a merging candidatelist to be described below and derive a reference block in which adifference from the current block is minimum or is equal to or less thana predetermined criterion among reference blocks indicated by mergecandidates included in the merging candidate list. In this case, a mergecandidate associated with the derived reference block may be selectedand merge index information indicating the selected merge candidate maybe generated and signaled to the decoding apparatus. The motioninformation of the current block may be derived by using the motioninformation of the selected merge candidate.

As another example, when an (A)MVP mode is applied to the current block,the encoding apparatus may configure an (A)MVP candidate list to bedescribed below and use a motion vector of a selected mvp candidateamong motion vector predictor (mvp) candidates included in the (A)MVPcandidate list as the mvp of the current block. In this case, forexample, the motion vector indicating the reference block derived by themotion estimation may be used as the motion vector of the current blockand an mvp candidate having a motion vector with a smallest differencefrom the motion vector of the current block among the mvp candidates maybecome the selected mvp candidate. A motion vector difference (MVD)which is a difference obtained by subtracting the mvp from the motionvector of the current block may be derived. In this case, theinformation on the MVD may be signaled to the decoding apparatus.Further, when the (A)MVP mode is applied, the value of the referencepicture index may be configured as reference picture index informationand separately signaled to the decoding apparatus.

The encoding apparatus may derive the residual samples based on thepredicted samples (S410). The encoding apparatus may derive the residualsamples by comparing original samples and the prediction samples of thecurrent block.

The encoding apparatus encodes image information including predictioninformation and residual information (S420). The encoding apparatus mayoutput the encoded image information in the form of a bit stream. Theprediction information may include information on prediction modeinformation (e.g., skip flag, merge flag or mode index, etc.) andinformation on motion information as information related to theprediction procedure. The information on the motion information mayinclude candidate selection information (e.g., merge index, mvp flag ormvp index) which is information for deriving the motion vector. Further,the information on the motion information may include the information onthe MVD and/or the reference picture index information. Further, theinformation on the motion information may include information indicatingwhether to apply the L0 prediction, the L1 prediction, or thebi-prediction. The residual information is information on the residualsamples. The residual information may include information on quantizedtransform coefficients for the residual samples.

An output bit stream may be stored in a (digital) storage medium andtransferred to the decoding apparatus or transferred to the decodingapparatus via the network.

Meanwhile, as described above, the encoding apparatus may generate areconstructed picture (including reconstructed samples and reconstructedblocks) based on the reference samples and the residual samples. This isto derive the same prediction result as that performed by the decodingapparatus, and as a result, coding efficiency may be increased.Accordingly, the encoding apparatus may store the reconstruction picture(or reconstruction samples or reconstruction blocks) in the memory andutilize the reconstruction picture as the reference picture. The in-loopfiltering process may be further applied to the reconstruction pictureas described above.

A video/image decoding process based on inter prediction mayschematically include, for example, the following.

FIG. 5 illustrates an example of an inter prediction-based video/imagedecoding method.

Referring to FIG. 5, the decoding apparatus may perform an operationcorresponding to the operation performed by the encoding apparatus. Thedecoding apparatus may perform the prediction for the current blockbased on received prediction information and derive the predictionsamples.

Specifically, the decoding apparatus may determine the prediction modefor the current block based on the received prediction information(S500). The decoding apparatus may determine which inter prediction modeis applied to the current block based on the prediction mode informationin the prediction information.

For example, it may be determined whether the merge mode or the (A)MVPmode is applied to the current block based on the merge flag.Alternatively, one of various inter prediction mode candidates may beselected based on the mode index. The inter prediction mode candidatesmay include a skip mode, a merge mode, and/or an (A)MVP mode or mayinclude various inter prediction modes to be described below.

The decoding apparatus derives the motion information of the currentblock based on the determined inter prediction mode (S510). For example,when the skip mode or the merge mode is applied to the current block,the decoding apparatus may configure the merge candidate list to bedescribed below and select one merge candidate among the mergecandidates included in the merge candidate list. Here, the selection maybe performed based on the selection information (merge index). Themotion information of the current block may be derived by using themotion information of the selected merge candidate. The motioninformation of the selected merge candidate may be used as the motioninformation of the current block.

As another example, when an (A)MVP mode is applied to the current block,the decoding apparatus may configure an (A)MVP candidate list to bedescribed below and use a motion vector of a selected mvp candidateamong motion vector predictor (mvp) candidates included in the (A)MVPcandidate list as the mvp of the current block. Here, the selection maybe performed based on the selection information (mvp flag or mvp index).In this case, the MVD of the current block may be derived based on theinformation on the MVD, and the motion vector of the current block maybe derived based on the mvp of the current block and the MVD. Further,the reference picture index of the current block may be derived based onthe reference picture index information. The picture indicated by thereference picture index in the reference picture list for the currentblock may be derived as the reference picture referred for the interprediction of the current block.

Meanwhile, as described below, the motion information of the currentblock may be derived without a candidate list configuration and in thiscase, the motion information of the current block may be derivedaccording to a procedure disclosed in the prediction mode. In this case,the candidate list configuration may be omitted.

The decoding apparatus may generate the prediction samples for thecurrent block based on the motion information of the current block(S520). In this case, the reference picture may be derived based on thereference picture index of the current block and the prediction samplesof the current block may be derived by using the samples of thereference block indicated by the motion vector of the current block onthe reference picture. In this case, in some cases, a predicted samplefiltering procedure for all or some of the prediction samples of thecurrent block may be further performed.

For example, the inter-prediction unit of the decoding apparatus mayinclude a prediction mode determination unit, a motion informationderivation unit, and a prediction sample derivation unit, and theprediction mode determination unit may determine the prediction mode forthe current block based on the received prediction mode information, themotion information derivation unit may derive the motion information(the motion vector and/or reference picture index) of the current blockbased on the information on the received motion information, and theprediction sample derivation unit may derive the predicted samples ofthe current block.

The decoding apparatus generates the residual samples for the currentblock based on the received residual information (S530). The decodingapparatus may generate the reconstruction samples for the current blockbased on the prediction samples and the residual samples and generatethe reconstruction picture based on the generated reconstruction samples(S540). Thereafter, the in-loop filtering procedure may be furtherapplied to the reconstruction picture as described above.

FIG. 6 schematically shows an inter prediction procedure.

Referring to FIG. 6, as described above, the inter prediction processmay include an inter prediction mode determination step, a motioninformation derivation step according to the determined prediction mode,and a prediction processing (prediction sample generation) step based onthe derived motion information. The inter prediction process may beperformed by the encoding apparatus and the decoding apparatus asdescribed above. In this document, a coding device may include theencoding apparatus and/or the decoding apparatus.

Referring to FIG. 6, the coding apparatus determines an inter predictionmode for the current block (S600). Various inter prediction modes may beused for the prediction of the current block in the picture. Forexample, various modes, such as a merge mode, a skip mode, a motionvector prediction (MVP) mode, an affine mode, a subblock merge mode, amerge with MVD (MMVD) mode, and a historical motion vector prediction(HMVP) mode may be used. A decoder side motion vector refinement (DMVR)mode, an adaptive motion vector resolution (AMVR) mode, a bi-predictionwith CU-level weight (BCW), a bi-directional optical flow (BDOF), andthe like may be further used as additional modes. The affine mode mayalso be referred to as an affine motion prediction mode. The MVP modemay also be referred to as an advanced motion vector prediction (AMVP)mode. In the present document, some modes and/or motion informationcandidates derived by some modes may also be included in one of motioninformation-related candidates in other modes. For example, the HMVPcandidate may be added to the merge candidate of the merge/skip modes,or also be added to an mvp candidate of the MVP mode. If the HMVPcandidate is used as the motion information candidate of the merge modeor the skip mode, the HMVP candidate may be referred to as the HMVPmerge candidate.

The prediction mode information indicating the inter prediction mode ofthe current block may be signaled from the encoding apparatus to thedecoding apparatus. In this case, the prediction mode information may beincluded in the bit stream and received by the decoding apparatus. Theprediction mode information may include index information indicating oneof multiple candidate modes. Alternatively, the inter prediction modemay be indicated through a hierarchical signaling of flag information.In this case, the prediction mode information may include one or moreflags. For example, whether to apply the skip mode may be indicated bysignaling a skip flag, whether to apply the merge mode may be indicatedby signaling a merge flag when the skip mode is not applied, and it isindicated that the MVP mode is applied or a flag for additionaldistinguishing may be further signaled when the merge mode is notapplied. The affine mode may be signaled as an independent mode orsignaled as a dependent mode on the merge mode or the MVP mode. Forexample, the affine mode may include an affine merge mode and an affineMVP mode.

The coding apparatus derives motion information for the current block(S610). Motion information derivation may be derived based on the interprediction mode.

The coding apparatus may perform inter prediction using motioninformation of the current block. The encoding apparatus may deriveoptimal motion information for the current block through a motionestimation procedure. For example, the encoding apparatus may search asimilar reference block having a high correlation in units of afractional pixel within a predetermined search range in the referencepicture by using an original block in an original picture for thecurrent block and derive the motion information through the searchedreference block. The similarity of the block may be derived based on adifference of phase based sample values. For example, the similarity ofthe block may be calculated based on a sum of absolute differences (SAD)between the current block (or a template of the current block) and thereference block (or the template of the reference block). In this case,the motion information may be derived based on a reference block havinga smallest SAD in a search area. The derived motion information may besignaled to the decoding apparatus according to various methods based onthe inter prediction mode.

The coding apparatus performs inter prediction based on motioninformation for the current block (S620). The coding apparatus mayderive prediction sample(s) for the current block based on the motioninformation. A current block including prediction samples may bereferred to as a predicted block.

Meanwhile, as described above, the encoding apparatus may performvarious encoding methods such as exponential Golomb, context-adaptivevariable length coding (CAVLC), and context-adaptive binary arithmeticcoding (CABAC). In addition, the decoding apparatus may decodeinformation in a bitstream based on a coding method such as exponentialGolomb coding, CAVLC or CABAC, and output a value of a syntax elementrequired for image reconstruction and quantized values of transformcoefficients related to residuals.

For example, the coding methods described above may be performed asdescribed below.

FIG. 7 exemplarily shows context-adaptive binary arithmetic coding(CABAC) for encoding a syntax element. For example, in the CABACencoding process, when an input signal is a syntax element, rather thana binary value, the encoding apparatus may convert the input signal intoa binary value by binarizing the value of the input signal. In addition,when the input signal is already a binary value (i.e., when the value ofthe input signal is a binary value), binarization may not be performedand may be bypassed. Here, each binary number 0 or 1 constituting abinary value may be referred to as a bin. For example, if a binarystring after binarization is 110, each of 1, 1, and 0 is called one bin.The bin(s) for one syntax element may indicate a value of the syntaxelement.

Thereafter, the binarized bins of the syntax element may be input to aregular coding engine or a bypass coding engine. The regular codingengine of the encoding apparatus may allocate a context model reflectinga probability value to the corresponding bin, and may encode thecorresponding bin based on the allocated context model. The regularcoding engine of the encoding apparatus may update a context model foreach bin after performing encoding on each bin. A bin encoded asdescribed above may be referred to as a context-coded bin.

Meanwhile, when the binarized bins of the syntax element are input tothe bypass coding engine, they may be coded as follows. For example, thebypass coding engine of the encoding apparatus omits a procedure ofestimating a probability with respect to an input bin and a procedure ofupdating a probability model applied to the bin after encoding. Whenbypass encoding is applied, the encoding apparatus may encode the inputbin by applying a uniform probability distribution instead of allocatinga context model, thereby improving an encoding rate. The bin encoded asdescribed above may be referred to as a bypass bin.

Entropy decoding may represent a process of performing the same processas the entropy encoding described above in reverse order.

For example, when a syntax element is decoded based on a context model,the decoding apparatus may receive a bin corresponding to the syntaxelement through a bitstream, determine a context model using the syntaxelement and decoding information of a decoding target block or aneighbor block or information of a symbol/bin decoded in a previousstage, predict an occurrence probability of the received bin accordingto the determined context model, and perform an arithmetic decoding onthe bin to derive a value of the syntax element. Thereafter, a contextmodel of a bin which is decoded next may be updated with the determinedcontext model.

Also, for example, when a syntax element is bypass-decoded, the decodingapparatus may receive a bin corresponding to the syntax element througha bitstream, and decode the input bin by applying a uniform probabilitydistribution. In this case, the procedure of the decoding apparatus forderiving the context model of the syntax element and the procedure ofupdating the context model applied to the bin after decoding may beomitted.

As described above, residual samples may be derived as quantizedtransform coefficients through transform and quantization processes. Thequantized transform coefficients may also be referred to as transformcoefficients. In this case, the transform coefficients in a block may besignaled in the form of residual information. The residual informationmay include a residual coding syntax. That is, the encoding apparatusmay configure a residual coding syntax with residual information, encodethe same, and output it in the form of a bitstream, and the decodingapparatus may decode the residual coding syntax from the bitstream andderive residual (quantized) transform coefficients. The residual codingsyntax may include syntax elements representing whether transform wasapplied to the corresponding block, a location of a last effectivetransform coefficient in the block, whether an effective transformcoefficient exists in the subblock, a size/sign of the effectivetransform coefficient, and the like, as will be described later.

For example, the (quantized) transformation coefficients (i.e., theresidual information) may be encoded and/or decoded based on syntaxelements such as transform_skip_flag, last_sig_coeff_x_prefix,last_sig_coeff_y_prefix, last_sig_coeff_x_suffix,last_sig_coeff_y_suffix, coded_sub_block_flag, sig_coeff_flag,par_level_flag, abs_level_gt1_flag, abs_level_gt3_flag, abs_remainder,coeff_sign_flag, dec_abs_level, mts_idx. Syntax elements related toresidual data encoding/decoding may be represented as shown in thefollowing table.

TABLE 1 Descriptor residual_coding( x0, y0, log2TbWidth, log2ThHeight,cIdx ) {  if( transform_skip_enabled_flag && ( cIdx ! = 0 | |tu_mts_flag[ x0 ][ y0 ] = = 0 ) &&   ( log2TbWidth <= 2 ) && (log2TbHeight <= 2 ) )   transform_skip_flag[ x0 ][ y0 ][ cIdx ] ae(v) last_sig_coeff_x_prefix ae(v)  last_sig_coeff_y_prefix ae(v)  if(last_sig_coeff_x_prefix > 3 )   last_sig_coeff_x_suffix ae(v)  if(last_sig_coeff_y_prefix > 3 )   last_sig_coeff_y_suffix ac(v) log2SbSize = ( Min( log2TbWidth, log2TbHeight ) < 2 ? 1 : 2 ) numSbCocff = 1 << ( log2SbSize << 1 )  lastScanPos = numSbCoeff lastSubBlock = ( 1 << ( log2TbWidth + log2TbHeight − 2 * log2SbSize, )) − 1  do {   if( lastScanPos = = 0 ) {    lastScanPos = numSbCoeff   lastSubBlock− −   }   lastScanPos− −   xS = DiagScanOrder[log2TbWidth − log2SbSize ][ log2TbHeight − log2SbSize ]          [lastSubBlock ][ 0 ]   yS = DiagScanOrder[ log2TbWidth − log2SbSize ][log2TbHeight − log2SbSize ]          [ lastSubBlock ][ 1 ]   xC = ( xS<< log2SbSize ) +     DiagScanOrder[ log2SbSize ][ log2SbSize ][lastScanPos ][ 0 ]   yC = ( yS << log2SbSize ) +     DiagScanOrder[log2SbSize ][ log2SbSize ][ lastScanPos ][ 1 ]  } while( ( xC !=LastSignificantCoeffX ) | | ( yC != LastSignificantCoeffY ) ) numSigCoeff = 0  QState = 0  for( i = lastSubBlock; i <= 0; 1− − ) {  startQStateSb = QState   xS = DiagScanOrder[ log2TbWidth − log2SbSize][ log2TbHeight − log2SbSize ]          [ lastSubBlock ][ 0 ]   yS =DiagScanOrder[ log2TbWidth − log2SbSize ][ log2TbHeight − log2SbSize]         [ lastSubBlock ][ 1 ]   inferSbDcSigCoeffFlag = 0   if( ( i <lastSubBlock ) && ( i > 0 ) ) {    coded_sub_block_flag[ xS ][ yS ]ae(v)    inferSbDcSigCoeffFlag = 1   }   firstSigScanPosSb = numSbCoeff  lastSigScanPosSb = −1   remBinsPass1 = ( log2SbSize < 2 ? 6 : 28 )  remBinsPass2 = ( log2SbSize < 2 ? 2: 4 )   firstPosMode0 = ( i = =lastSubBlock ? lastScanPos − 1 : numSbCoeff − 1 )   firstPosMode1 − −1  firstPosMode2 = −1   for( n = ( i = = firstPosMode0; n >= 0 &&remBinsPass1 >= 3; n− − ) {    xC = ( xS << log2SbSize ) +DiagScanOrder[ log2SbSize ][ log2SbSize ][ n ][ 0 ]    yC = ( yS <<log2SbSize ) + DiagScanOrder[ log2SbSize ][ log2SbSize ][ n ][ 1]    if(coded_sub_block_flag[ xS ][ yS ] && ( n > 0 | | !inferSbDcSigCoeffFlag )) {     sig_coeff_flag[ xC ][ yC ] ae(v)     remBinsPass1− −     if(sig_coeff_flag[ xC ][ yC ] )       inferSbDcSigCoeffFlag = 0    }    if(sig_coeff_flag[ xC ][ yC ] ) {     numSigCoeff++     abs_level_gt1_flag[n] ae(v)     remBinsPass1− −     if( abs_level_gt1_flag[ n] ) {      par_level_flag[ n] ae(v)       remBinsPass1       if(remBinsPass2 > 0 ) {        remBinsPass2− −        if( remBinsPass2 = =0 )         firstPosMode1 = n − 1       }     }     if( lastSigScanPosSb= = −1 )       lastSigScanPosSb = n     firstSigScanPosSb = n    }   AbsLevelPass1[ xC ][ yC ] =       sig_coeff_flag[ xC ][ yC ] +par_level_flag[ n ] + abs_level_gt1_flag[ n ]    if(dep_quant_enabled_flag )     QState = QStateTransTable[ QState ][AbsLevelPass1[ xC ][ yC ] & 1 ]    if( remBinsPass1 < 3 )    firstPosMode2 = n − 1   }   if( firstPosMode1 < firstPosMode2 )   firstPosMode1 = firstPosMode2   for( n = numSbCoeff − 1; n >=firstPosMode2; n− − )    if( abs_level_gt1_flag,[ n ] )    abs_level_gt3_flag[ n ] ae(v)   for( n = numSbCoeff − 1; n >=firstPosMode1; n− − ) {    xC = ( xS << log2SbSize ) + DiagScanOrder ][log2SbSize ][ log2SbSize ][ n ][ 0 ]    yC = ( yS << log2SbSize ) +DiagScanOrder ][ log2SbSize ][ log2SbSize ][ n ][ 1 ]    if(abs_level_gt3_flag[n ] )     abs_remainder[ n ] ae(v)    AbsLevel[ xC ][yC ] = AbsLevelPass1[ xC ][ yC ] +           2 * ( abs_level_gt3_flag[ n] + abs_remainder[ n ] )   }   for( n = firstPosMode1; n >firstPosMode2; n− − ) {    xC = ( xS << log2SbSize ) + DiagScanOrder[log2SbSize ][ log2SbSize ][ n ][ 0 ]    yC = ( yS << log2SbSize ) +DiagScanOrder[ log2SbSize ][ log2SbSize ][ n ][ 1 ]    if(abs_level_gt1_flag[ n ] )     abs_remainder[ n ] ae(v)    AbsLevel[ xC][ yC ] = AbsLevelPass1[ xC ][ yC ] | 2 * abs_remainder[ n ]   }   for(n = firstPosMode2; n >= 0; n ) {    XC = ( xS << log2SbSize ) +DiagScanOrder[ log2SbSize ][ log2SbSize ][ n ][ 0 ]    yC = ( yS <<log2SbSize ) + DiagScanOrder[ log2SbSize ][ log2SbSize ][ n ][ 1 ]   dec_abs_level[ n ] ae(v)    if( AbsLevel[ xC ][ yC ] > 0 )    firstSigScanPosSb = n    if( dep_quant_enabled_flag )     QState =QStateTransTable[ QState ][ AbsLevel[ xC ][ yC ] & 1 ]   }   if(dep_quant_enabled_flag | !sign_data_hiding_enabled_flag )    signHidden= 0   else    signHidden = ( lastSigScanPosSb − firstSigScanPosSb > 3 ?1 : 0 )   for( n = numSbCoeff − 1; n >= 0; n− − ) {    xC = ( xS <<log2SbSize ) + DiagScanOrder[ log2SbSize ][ log2SbSize ][ n ][ 0 ]    yC= ( yS << log2SbSize ) + DiagScanOrder[ log2SbSize ][ log2SbSize ][ n ][1 ]    if( sig_coeff_flag[ xC ][ yC ] &&     ( !signHidden | | ( n !=firstSigScanPosSb ) ) )     coeff sign flag[ n ] ae(v)   }   if(dep_quant_enabled_flag ) {    QState = startQStateSb    for( n =numSbCoeff − 1; n >= 0; n − − ) {     xC = ( xS << log2SbSize ) +       DiagScanOrder[ log2SbSize ][ log2SbSize ][ n ][ 0 ]     yC = ( yS<< log2SbSize ) +        DiagScanOrder[ log2SbSize ][ log2SbSize ][ n ][1 ]     if( sig_coeff_flag[ xC ][ yC ] )       TransCoeffLevel[ x0 ][ y0][ cIdx ][ xC ][ yC ] =         ( 2 * AbsLevel[ xC ][ yC ]− ( QState > 1? 1 : 0 ) ) *         ( 1 − 2 * coeff_sign_flag[ n ] )     QState =QStateTransTable[ QState ][ par_level_flag[ n ] ]   } else {   sumAbsLevel = 0    for( n = numSbCoeff− 1; n >= 0; n − − ) {     xC =( xS << log2SbSize ) +        DiagScanOrded[ log2SbSize ][ log2SbSize ][n ][ 0 ]     yC = ( yS << log2SbSize ) +        DiagScanOrder[log2SbSize ][ log2SbSize ][ n ][ 1 ]     if( sig_coeff_flag[ xC ][ yC ]) {       TransCoeffLevel[ x0 ][ y0 ][ cIdx ][ xC ][ yC ] =        AbsLevel[ xC ][ yC ] * ( 1 2 * coeff_sign_flag[ n ] )       if(signHidden ) {        sumAbsLevel −= AbsLevel[ xC ][ yC ]        if( ( n= = firstSigScanPosSb ) && ( sumAbsLevel % 2 ) = = 1 ) )        TransCoeffLevel[ x0 ][ y0 ][ cIdx ][ xC ][ yC ] =          −TransCoeffLevel[ x0 ][ y0 ][ cIdx ][ xC ][ yC ]       }     }   }   }  }  if( tu_mts_flag[ x0 ][ y0 ] && ( cIdx = = 0 ) )   mts_idx[x0 ][ y0 ][ cIdx ] ae(v) }

transform_skip_flag indicates whether transform is skipped in anassociated block. The transform_skip_flag may be a syntax element of atransform skip flag. The associated block may be a coding block (CB) ora transform block (TB). Regarding transform (and quantization) andresidual coding procedures, CB and TB may be used interchangeably. Forexample, as described above, residual samples may be derived for CB, and(quantized) transform coefficients may be derived through transform andquantization for the residual samples, and through the residual codingprocedure, information (e.g., syntax elements) efficiently indicating aposition, magnitude, sign, etc. of the (quantized) transformcoefficients may be generated and signaled. The quantized transformcoefficients may simply be called transform coefficients. In general,when the CB is not larger than a maximum TB, a size of the CB may be thesame as a size of the TB, and in this case, a target block to betransformed (and quantized) and residual coded may be called a CB or aTB. Meanwhile, when the CB is greater than the maximum TB, a targetblock to be transformed (and quantized) and residual coded may be calleda TB. Hereinafter, it will be described that syntax elements related toresidual coding are signaled in units of transform blocks (TBs) but thisis an example and the TB may be used interchangeably with coding blocks(CBs as described above.

Meanwhile, syntax elements which are signaled after the transform skipflag is signaled may be the same as the syntax elements disclosed inTable 2 below, and detailed descriptions on the syntax elements aredescribed below.

TABLE 2 Descriptor transform_unit( x0, y0, tbWidth, tbHeight, treeType,subTuIndex, chType ) {  if( IntraSubPartitionsSplitType != ISP_NO_SPLIT&&    treeType = = SINGLE_TREE && subTuIndex = = NumIntraSubPartiti ons− 1 ) {   xC = CbPosX[ chType ][ x0 ][ y0 ]   yC = CbPosY[ chType ][ x0][ y0 ]   wC = CbWidth[ chType ][ x0 ][ y0 ] / SubWidthC   hC =CbHeight[ chType ][ x0 ][ y0 ] / SubHeightC  } else {   xC = x0   yC =y0   wC = tbWidth / SubWidthC   hC = tbHeight / SubHeightC  } chromaAvailable = treeType != DUAL_TREE_LUMA && sps_chroma_form at_idc!= 0 &&   ( IntraSubPartitionsSplitType = = ISP_NO_SPLIT | |   (IntraSubPartitionsSplitType != ISP_NO_SPLIT &&   subTuIndex = =NumIntraSubPartitions − 1 ) )  if( ( treeType = = SINGLE_TREE | |treeType = = DUAL_TREE_CHROM A ) &&    sps_chroma_format_idc != 0 &&   ( ( IntraSubPartitionsSplitType = = ISP_NO_SPLIT && !( cu_sbt_flag &&   ( ( subTuIndex = = 0 && cu_sbt_pos_flag ) | |    ( subTuIndex = = 1&& !cu_sbt_pos_flag ) ) ) ) | |    ( IntraSubPartitionsSplitType !=ISP_NO_SPLIT &&    ( subTuIndex = = NumIntraSubPartitions − 1 ) ) ) ) {  tu_cb_coded_flag[ xC ][ yC ] ae(v)   tu_cr_coded_flag[ xC ][ yC ]ae(v)  }      if( treeType = = SINGLE_TREE | | treeType = =DUAL_TREE_LUMA ) {       if( ( IntraSubPartitionsSplitType = =ISP_NO_SPLIT && !( cu_sbt_flag &     &         ( ( subTuIndex = = 0 &&cu_sbt_pos_flag ) | |         ( subTuIndex = = 1 && !cu_sbt_pos_flag ) )) &&         ( ( CuPredMode[ chType ][ x0 ][ y0 ] = = MODE_INTRA &&        !cu_act_enabled_flag[ x0 ][ y0 ] ) | |         ( chromaAvailable&& ( tu_cb_coded_flag[ xC ][ yC ] | |         tu_cr_coded_flag[ xC ][ yC] ) ) | |         CbWidth[ chType ][ x0 ][ y0 ] > MaxTbSizeY | |        CbHeight[ chType ][ x0 ][ y0 ] > MaxTbSizeY ) ) | |         (IntraSubPartitionsSplitType != ISP_NO_SPLIT &&         ( subTuIndex <NumIntraSubPartitions − 1 | | !InferTuCbfLuma ) ) )       tu_y_coded_flag[ x0 ][ y0 ] ae(v)      if(IntraSubPartitionsSplitType != ISP_NO_SPLIT )       InferTuCbfLuma = InferTuCbfLuma && !tu_y_coded_flag[ x0 ][ y0 ]     }      if( ( CbWidth[ chType ][ x0 ][ y0 ] > 64 | | CbHeight[chType ][ x0 ][ y     0 ] > 64 | |        tu_y_coded_flag[ x0 ][ y0 ] || ( chromaAvailable && ( tu_cb_coded_flag     [ xC ][ yC ] | |       tu_cr_coded_flag[ xC ][ yC ] ) ) && treeType != DUAL_TREE_CHRO    MA &&        pps_cu_qp_delta_enabled_flag && !IsCuQpDeltaCoded ) {      cu_qp_delta_abs ae(v)       if( cu_qp_delta_abs )       cu_qp_delta_sign_flag ae(v)      }      if( ( CbWidth[ chType ][x0 ][ y0 ] > 64 | | CbHeight[ chType ][ x0 ][ y     0 ] > 64 | |       ( chromaAvailable && ( tu_cb_coded_flag[ xC ][ yC ] | |       tu_cr_coded_flag[ xC ][ yC ] ) ) ) &&        treeType !=DUAL_TREE_LUMA && sh_cu_chroma_qp_offset_enable     d_flag &&       !IsCuChromaQpOffsetCoded ) {       cu_chroma_qp_offset_flag ae(v)      if( cu_chroma_qp_offset_flag &&pps_chroma_qp_offset_list_len_minus1 >     0 )       cu_chroma_qp_offset_idx ae(v)      }      if(sps_joint_cbcr_enabled_flag && ( ( CuPredMode[ chType ][ x0 ][ y0 ] = =    MODE_INTRA        && ( tu_cb_coded_flag[ xC ][ yC ] | |tu_cr_coded_flag[ xC ][ yC ] ) ) | |        ( tu_cb_coded_flag[ xC ][ yC] && tu_cr_coded_flag[ xC ][ yC ] ) ) &&        chromaAvailable )      tu_joint_cbcr_residual_flag[ xC ][ yC ] ae(v)      if(tu_y_coded_flag[ x0 ][ y0 ] && treeType != DUAL_TREE_CHROMA ) {      if( sps_transform_skip_enabled_flag && !BdpcmFlag[ x0 ][ y0 ][ 0 ]&&         tbWidth <= MaxTsSize && tbHeight <= MaxTsSize &&         (IntraSubPartitionsSplitType = = ISP_NO_SPLIT ) && !cu_sbt_flag )       transform_skip_flag[ x0 ][ y0 ][ 0 ] ae(v)       if(!transform_skip_flag[ x0 ][ y0 ][ 0 ] | |sh_ts_residual_coding_disabled_fla     g )         residual_coding( x0,y0, Log2( tbWidth ), Log2( tbHeight ), 0 )       else       residual_ts_coding( x0, y0, Log2( tbWidth ), Log2( tbHeight ), 0)      }      if( tu_cb_coded_flag[ xC ][ yC ] && treeType !=DUAL_TREE_LUMA ) {       if( sps_transform_skip_enabled_flag &&!BdpcmFlag[ x0 ][ y0 ][ 1 ] &&         wC <= MaxTsSize && hC <=MaxTsSize && !cu_sbt_flag )        transform_skip_flag[ xC ][ yC ][ 1 ]ae(v)       if( !transform_skip_flag[ xC ][ yC ][ 1 ] | |sh_ts_residual_coding_disabled_fl     ag )        residual_coding( xC,yC, Log2( wC ), Log2( hC ), 1 )       else        residual_ts_coding(xC, yC, Log2( wC ), Log2( hC ), 1 )      }      if( tu_cr_coded_flag[ xC][ yC ] && treeType != DUAL_TREE_LUMA &&        !( tu_cb_coded_flag[ xC][ yC ] && tu_joint_cbcr_residual_flag[ xC ][ y     C ] ) ) {     C ] )) {       if( sps_transform_skip_enabled_flag && !BdpcmFlag[ x0 ][ y0 ][2 ] &&         wC <= MaxTsSize && hC <= MaxTsSize && !cu_sbt_flag )       transform_skip_flag[ xC ][ yC ][ 2 ] ae(v)       if(!transform_skip_flag[ xC ][ yC ][ 2 ] | |sh_ts_residual_coding_disabled_fl     ag )        residual_coding( xC,yC, Log2( wC ), Log2( hC ), 2 )       else        residual_ts_coding(xC, yC, Log2( wC ), Log2( hC ), 2 )      }     }

TABLE 3 Descriptor residual_coding( x0, y0, log2TbWidth, log2TbHeight,cIdx ) {  if( sps_mts_enabled_flag && cu_sbt_flag && cIdx = = 0 &&   log2TbWidth = = 5 && log2TbHeight < 6 )   log2ZoTbWidth = 4  else  log2ZoTbWidth = Min( log2TbWidth, 5 )  if( sps_mts_enabled_flag &&cu_sbt_flag && cIdx = = 0 &&    log2TbWidth < 6 && log2TbHeight = = 5 )  log2ZoTbHeight = 4  else   log2ZoTbHeight = Min( log2TbHeight, 5 ) if( log2TbWidth > 0 )   last_sig_coeff_x_prefix ae(v)  if(log2TbHeight > 0 )   last_sig_coeff_y_prefix ae(v)  if(last_sig_coeff_x_prefix > 3 )   last_sig_coeff_x_suffix ae(v)  if(last_sig_coeff_y_prefix > 3 )   last_sig_coeff_y_suffix ae(v) log2TbWidth = log2ZoTbWidth  log2TbHeight = log2ZoTbHeight remBinsPass1 = ( ( 1 << ( log2TbWidth + log2TbHeight ) ) * 7 ) >> 2 log2SbW = ( Min( log2TbWidth, log2TbHeight ) < 2 ? 1 : 2 )  log2SbH =log2SbW  if( log2TbWidth + log2TbHeight > 3 )   if( log2TbWidth < 2 ) {   log2SbW = log2TbWidth    log2SbH = 4 − log2SbW   } else if(log2TbHeight < 2 ) {    log2SbH = log2TbHeight    log2SbW = 4 − log2SbH  }  numSbCoeff = 1 << ( log2SbW + log2SbH )  lastScanPos = numSbCoeff lastSubBlock = ( 1 << ( log2TbWidth + log2TbHeight − ( log2SbW + log2SbH ) ) ) − 1      do {       if( lastScanPos = = 0 ) {        lastScanPos= numSbCoeff        lastSubBlock− −       }       lastScanPos− −      xS = DiagScanOrder[ log2TbWidth − log2SbW ][ log2TbHeight −log2SbH ]            [ lastSubBlock ][ 0 ]       yS = DiagScanOrder[log2TbWidth − log2SbW ][ log2TbHeight − log2SbH ]            [lastSubBlock ][ 1 ]       xC = ( xS << log2SbW ) + DiagScanOrder[log2SbW ][ log2SbH ][ lastScan     Pos ][ 0 ]       yC = ( yS << log2SbH) + DiagScanOrder[ log2SbW ][ log2SbH ][ lastScan     Pos ][ 1 ]      }while( ( xC != LastSignificantCoeffX ) | | ( yC != LastSignificantCoeffY)     )      if( lastSubBlock = = 0 && log2TbWidth >= 2 &&log2TbHeight >= 2 &     &        !transform_skip_flag[ x0 ][ y0 ][ cIdx] && lastScanPos > 0 )       LfnstDcOnly = 0      if( ( lastSubBlock > 0&& log2TbWidth >= 2 && log2TbHeight >= 2 ) | |        ( lastScanPos > 7&& ( log2TbWidth = = 2 | | log2TbWidth = = 3 ) &     &       log2TbWidth = = log2TbHeight ) )       LfnstZeroOutSigCoeffFlag =0      if( ( lastSubBlock > 0 | | lastScanPos > 0 ) && cIdx = = 0 )      MtsDcOnly = 0      QState = 0      for( i = lastSubBlock; i >= 0;i− − ) {       startQStateSb = QState       xS = DiagScanOrder[log2TbWidth − log2SbW ][ log2TbHeight − log2SbH ]            [ i ][ 0 ]      yS = DiagScanOrder[ log2TbWidth − log2SbW ][ log2TbHeight −log2SbH ]            [ i ][ 1 ]       inferSbDcSigCoeffFlag = 0      if( i < lastSubBlock && i > 0 ) {        sb_coded_flag[ xS ][ yS ]ae(v)        inferSbDcSigCoeffFlag = 1       }       if( sb_coded_flag[xS ][ yS ] && ( xS > 3 | | yS > 3 ) && cIdx = = 0 )       MtsZeroOutSigCoeffFlag = 0       firstSigScanPosSb = numSbCoeff      lastSigScanPosSb = −1       firstPosMode0 = ( i = = lastSubBlock ?lastScanPos : numSbCoeff − 1 )       firstPosMode1 = firstPosMode0      for( n = firstPosMode0; n >= 0 && remBinsPass1 >= 4; n− − ) {       xC = ( xS << log2SbW ) + DiagScanOrder[ log2SbW ][ log2SbH ][ n ]    [ 0 ]        yC = ( yS << log2SbH) + DiagScanOrder[ log2SbW ][log2SbH ][ n ]     [ 1 ]        if( sb_coded_flag[ xS ][ yS ] && ( n > 0| | !interSbDcSigCoeffFlag ) &     &          ( xC !=LastSignificantCoeffX | | yC != Last SignificantCoeffY ) )     {        sig_coeff_flag[ xC ][ yC ] ae(v)         remBinsPass1− −        if( sig_coeff_flag[ xC ][ yC ] )          inferSbDcSigCoeffFlag= 0        }        if( sig_coeff_flag[ xC ][ yC ] ) {        abs_level_gtx_flag[ n ][ 0 ] ae(v)         remBinsPass1− −        if( abs_level_gtx_flag[ n ][ 0 ] ) {          par_level_flag[ n] ae(v)          remBinsPass1− −          abs_level_gtx_flag[ n ][ 1 ]ae(v)          remBinsPass1− −         }         if( lastSigScanPosSb == −1 )          lastSigScanPosSb = n         firstSigScanPosSb = n       }        AbsLevelPass1[ xC ][ yC ] = sig_coeff_flag[ xC ][ yC ] +par_level_flag     [ n ] +             abs_level_gtx_flag[ n ][ 0 ] +2 * abs_level_gtx flag[ n ]     [ 1 ]        if( sh_dep_quant_used_flag)         QState = QStateTransTable[ QState ][ AbsLevelPass1[ xC ][ yC ]& 1 ]        firstPosMode1 = n − 1       }       for( n = firstPosMode0;n > firstPosMode1; n− − ) {        xC = ( xS << log2SbW ) +DiagScanOrder[ log2SbW ][ log2SbH ][ n ]     [ 0 ]        yC = ( yS <<log2SbH ) + DiagScanOrder[ log2SbW ][ log2SbH ][ n ]     [ 1 ]       if( abs_level_gtx_flag[ n ][ 1 ] )         abs_remainder[ n ]ae(v)        AbsLevel[ xC ][ yC ] = AbsLevelPass1[ xC ][ yC ] +2 *abs_remainder[ n ]       }       for( n = firstPosMode1; n >= 0; n− − ){        xC = ( xS << log2SbW ) + DiagScanOrder[ log2SbW ][ log2SbH ][ n]     [ 0 ]        yC = ( yS << log2SbH ) + DiagScanOrder[ log2SbW ][log2SbH ][ n ]     [ 1 ]        if( sb_coded_flag[ xS ][ yS ] )        dec_abs_level[ n ] ae(v)        if( AbsLevel[ xC ][ yC ] > 0 ) {        if( lastSigScanPosSb = = −1 )          lastSigScanPosSb = n        firstSigScanPosSb = n        }        if( sh_dep_quant_used_flag)         QState = QStateTransTable[ QState ][ AbsLevel[ xC ][ yC ] & 1]       }       if( sh_dep_quant_used_flag | |!sh_sign_data_hiding_used_flag )        signHidden = 0       else       signHidden = ( lastSigScanPosSb − firstSigScanPosSb > 3 ? 1 : 0 )      for( n = numSbCoeff − 1; n >= 0; n− − ) {        xC = ( xS <<log2SbW ) + DiagScanOrder[ log2SbW ][ log2SbH ][ n ]     [ 0 ]        yC= ( yS << log2SbH ) + DiagScanOrder[ log2SbW ][ log2SbH ][ n ]     [ 1 ]       if( ( AbsLevel[ xC ][ yC ] > 0 ) &&         ( !signHidden | | ( n!= firstSigScanPosSb ) ) )         coeff_sign_flag[ n ] ae(v)       }      if( sh_dep_quant_used_flag ) {        QState = startQStateSb       for( n = numSbCoeff − 1; n >= 0; n− − ) {         xC = ( xS <<log2SbW ) + DiagScanOrder[ log2SbW ][ log2SbH ][ n ]     [ 0 ]        yC = ( yS << log2SbH ) + DiagScanOrder[ log2SbW ][ log2SbH ][ n]     [ 1 ]         if( AbsLevel[ xC ][ yC ] > 0 )         TransCoeffLevel[ x0 ][ y0 ][ cIdx ][ xC ][ yC ] =            (2 * AbsLevel[ xC ][ yC ] − ( QState > 1 ? 1 : 0 ) ) *            ( 1 −2 * coeff_sign_flag[ n ] )         QState = QStateTransTable[ QState ][AbsLevel[ xC ][ yC ] & 1 ]       } else {        sumAbsLevel = 0       for( n = numSbCoeff − 1; n >= 0; n− − ) {         xC = ( xS <<log2SbW ) + DiagScanOrder[ log2SbW ][ log2SbH ][ n ]     [ 0 ]        yC = ( yS << log2SbH ) + DiagScanOrder[ log2SbW ][ log2SbH ][ n]     [ 1 ]         if( AbsLevel[ xC ][ yC ] > 0 ) {         TransCoeffLevel[ x0 ][ y0 ][ cIdx ][ xC ][ yC ] =           AbsLevel[ xC ][ yC ] * ( 1 − 2 * coeff_sign_flag[ n ] )         if( signHidden ) {           sumAbsLevel += AbsLevel[ xC ][ yC]           if( ( n = = firstSigScanPosSb ) && ( sumAbsLevel % 2 ) = = 1)     )            TransCoeffLevel[ x0 ][ y0 ][ cIdx ][ xC ][ yC ] =             −TransCoeffLevel[ x0 ][ y0 ][ cIdx ][ xC ][ yC ]          }        }        }       }      }     }

TABLE 4 Descriptor residual_ts_coding( x0, y0, log2TbWidth,log2TbHeight, cIdx ) {  log2SbW = ( Min( log2TbWidth, log2TbHeight ) < 2? 1 : 2 )  log2SbH = log2SbW  if( log2TbWidth + log2TbHeight > 3 )   if(log2TbWidth < 2 ) {    log2SbW = log2TbWidth    log2SbH = 4 − log2SbW  } else if( log2TbHeight < 2 ) {    log2SbH = log2TbHeight    log2SbW =4 − log2SbH   }  numSbCoeff = 1 << ( log2SbW + log2SbH )  lastSubBlock =( 1 << ( log2TbWidth + log2TbHeight − ( log2SbW + log2Sb H ) ) ) − 1 inferSbCbf = 1  RemCcbs = ( ( 1 << ( log2TbWidth + log2TbHeight ) ) * 7) >> 2  for( i =0; i <= lastSubBlock; i++ ) {   xS = DiagScanOrder[log2TbWidth − log2SbW ][ log2TbHeight − log2SbH ] [ i ][ 0 ]   yS =DiagScanOrder[ log2TbWidth − log2SbW ][ log2TbHeight − log2SbH ] [ i ][1 ]   if( i != lastSubBlock | | !inferSbCbf )    sb_coded_flag[ xS ][ yS] ae(v)   if( sb_coded_flag[ xS ][ yS ] && i < lastSubBlock )    inferSbCbf = 0  /* First scan pass */   inferSbSigCoeffFlag = 1  lastScanPosPass1 = −1   for( n = 0; n <= numSbCoeff − 1 && RemCcbs >=4; n++ ) {    xC = ( xS << log2SbW ) + DiagScanOrder[ log2SbW ][ log2SbH][ n ] [ 0 ]    yC = ( yS << log2SbH ) + DiagScanOrder[ log2SbW ][log2SbH ][ n ] [ 1 ]    lastScanPosPass1 = n        if( sb_coded_flag[xS ][ yS ] &&          ( n != numSbCoeff − 1 | | !inferSbSigCoeffFlag )) {         sig_coeff_flag[ xC ][ yC ] ae(v)         RemCcbs− −        if( sig_coeff_flag[ xC ][ yC ] )          inferSbSigCoeffFlag =0        }        CoeffSignLevel[ xC ][ yC ] = 0        if(sig_coeff_flag[ xC ][ yC ] ) {         coeff_sign_flag[ n ] ae(v)        RemCcbs− −         CoeffSignLevel[ xC ][ yC ] = (coeff_sign_flag[ n ] > 0 ? −1 : 1 )         abs_level_gtx_flag[ n ][ 0 ]ae(v)         RemCcbs− −         if( abs_level_gtx_flag[ n ][ 0 ] ) {         par_level_flag[ n ] ae(v)          RemCcbs− −         }       }        AbsLevelPass1[ xC ][ yC ] =          sig_coeff_flag[ xC][ yC ] + par_level_flag[ n ] + abs_level_gtx_flag     [ n ][ 0 ]      }      /* Greater than X scan pass (numGtXFlags=5) */      lastScanPosPass2 = −1       for( n = 0; n <= numSbCoeff − 1 &&RemCcbs >= 4; n++ ) {        xC = ( xS << log2SbW ) + DiagScanOrder[log2SbW ][ log2SbH ][ n ]     [ 0 ]        yC = ( yS << log2SbH ) +DiagScanOrder[ log2SbW ][ log2SbH ][ n ]     [ 1 ]        AbsLevelPass2[xC ][ yC ] = AbsLevelPass1[ xC ][ yC ]        for( j = 1; j < 5; j++ ) {        if( abs_level_gtx_flag[ n ][ j − 1 ] ) {         abs_level_gtx_flag[ n ][ j ] ae(v)          RemCcbs− −        }         AbsLevelPass2[ xC ][ yC ] += 2 * abs_level_gtx_flag[ n][ j ]        }        lastScanPosPass2 = n       }      /* remainderscan pass */       for( n = 0; n <= numSbCoeff − 1; n++ ) {        xC =( xS << log2SbW ) + DiagScanOrder[ log2SbW ][ log2SbH ][ n ]     [ 0 ]       yC = ( yS << log2SbH ) + DiagScanOrder[ log2SbW ][ log2SbH ][ n ]    [ 1 ]        if( ( n <= lastScanPosPass2 && AbsLevelPass2[ xC ][ yC] >= 10 ) | |          ( n > lastScanPosPass2 && n <= lastScanPosPass1&&          AbsLevelPass1[ xC ][ yC ] >= 2 ) | |          ( n >lastScanPosPass1 && sb_coded_flag[ xS ][ yS ] ) )         abs_remainder[n ] ae(v)        if( n <= lastScanPosPass2 )         AbsLevel[ xC ][ yC] = AbsLevelPass2[ xC ][ yC ] + 2 * abs_remainder     [ n ]        elseif(n <= lastScanPosPass1 )         AbsLevel[ xC ][ yC ] = AbsLevelPass1[xC ][ yC ] + 2 * abs_remainder     [ n ]        else { /* bypass */        AbsLevel[ xC ][ yC ] = abs_remainder[ n ]         if(abs_remainder[ n ] )          coeff_sign_flag[ n ] ae(v)        }       if( BdpcmFlag[ x0 ][ y0 ][ cIdx ] = = 0 && n <= lastScanPosPass1) {         absLeftCoeff = xC > 0 ? AbsLevel[ xC − 1 ][ yC ] ) : 0        absAboveCoeff = yC > 0 ? AbsLevel[ xC ][ yC − 1 ] ) : 0        predCoeff = Max( absLeftCoeff, absAboveCoeff )         if(AbsLevel[ xC ][ yC ] = = 1 && predCoeff > 0 )          AbsLevel[ xC ][yC ] = predCoeff         else if( AbsLevel[ xC ][ yC ] > 0 && AbsLevel[xC ][ yC ] <= predCo     eff )          AbsLevel[ xC ][ yC ]− −        }       TransCoeffLevel[ x0 ][ y0 ][ cIdx ][ xC ][ yC ] = ( 1 − 2 *coeff_sign_flag     [ n ] ) *          AbsLevel[ xC ][ yC ]       }     }     }

According to the present embodiment, as shown in Table 2, residualcoding may be divided according to a value of the syntax elementtransform_skip_flag of the transform skip flag. That is, a differentsyntax element may be used for residual coding based on the value of thetransform skip flag (based on whether the transform is skipped).Residual coding used when the transform skip is not applied (that is,when the transform is applied) may be called regular residual coding(RRC), and residual coding used when the transform skip is applied (thatis, when the transform is not applied) may be called transform skipresidual coding (TSRC). Also, the regular residual coding may bereferred to as general residual coding. Also, the regular residualcoding may be referred to as a regular residual coding syntax structure,and the transform skip residual coding may be referred to as a transformskip residual coding syntax structure. Table 3 above may show a syntaxelement of residual coding when a value of transform_skip_flag is 0,that is, when the transform is applied, and Table 4 above may show asyntax element of residual coding when the value of transform skip flagis 1, that is, when the transform is not applied.

Specifically, for example, the transform skip flag indicating whether toskip the transform of the transform block may be parsed, and whether thetransform skip flag is 1 may be determined. If the value of thetransform skip flag is 0, as shown in Table 3, syntax elementslast_sig_coeff_x_prefix, last_sig_coeff_y_prefix,last_sig_coeff_x_suffix, last_sig_coeff_y_suffix, sb_coded_flag,sig_coeff_flag, abs_level_gtx_flag, par_level_flag, abs_remainder,coeff_sign_flag and/or dec_abs_level for a residual coefficient of thetransform block may be parsed, and the residual coefficient may bederived based on the syntax elements. In this case, the syntax elementsmay be sequentially parsed, and a parsing order may be changed. Inaddition, the abs_level_gtx_flag may represent abs_level_gt1_flag,and/or abs_level_gt3_flag. For example, abs_level_gtx_flag[n][0] may bean example of a first transform coefficient level flag(abs_level_gt1_flag), and the abs_level_gtx_flag[n][1] may be an exampleof a second transform coefficient level flag (abs_level_gt3_flag).

Referring to the Table 3 above, last_sig_coeff_x_prefix,last_sig_coeff_y_prefix, last_sig_coeff_x_suffix,last_sig_coeff_y_suffix, sb_coded_flag, sig_coeff_flag,abs_level_gt1_flag, par_level_flag, abs_level_gt3_flag, abs_remainder,coeff_sign_flag, and/or dec_abs_level may be encoded/decoded. Meanwhile,sb_coded_flag may be represented as coded_sub_block_flag.

In an embodiment, the encoding apparatus may encode (x, y) positioninformation of the last non-zero transform coefficient in a transformblock based on the syntax elements last_sig_coeff_x_prefix,last_sig_coeff_y_prefix, last_sig_coeff_x_suffix, andlast_sig_coeff_y_suffix. More specifically, the last_sig_coeffx_prefixrepresents a prefix of a column position of a last significantcoefficient in a scanning order within the transform block, thelast_sig_coeff_y_prefix represents a prefix of a row position of thelast significant coefficient in the scanning order within the transformblock, the last_sig_coeff_x_suffix represents a suffix of a columnposition of the last significant coefficient in the scanning orderwithin the transform block, and the last_sig_coeff_y_suffix represents asuffix of a row position of the last significant coefficient in thescanning order within the transform block. Here, the significantcoefficient may represent a non-zero coefficient. In addition, thescanning order may be a right diagonal scanning order. Alternatively,the scanning order may be a horizontal scanning order or a verticalscanning order. The scanning order may be determined based on whetherintra/inter prediction is applied to a target block (a CB or a CBincluding a TB) and/or a specific intra/inter prediction mode.

Thereafter, the encoding apparatus may divide the transform block into4×4 sub-blocks, and then indicate whether there is a non-zerocoefficient in the current sub-block using a 1-bit syntax elementcoded_sub_block_flag for each 4×4 sub-block.

If a value of coded_sub_block_flag is 0, there is no more information tobe transmitted, and thus, the encoding apparatus may terminate theencoding process on the current sub-block. Conversely, if the value ofcoded_sub_block_flag is 1, the encoding apparatus may continuouslyperform the encoding process on sig_coeff_flag. Since the sub-blockincluding the last non-zero coefficient does not require encoding forthe coded_sub_block_flag and the sub-block including the DC informationof the transform block has a high probability of including the non-zerocoefficient, coded_sub_block_flag may not be coded and a value thereofmay be assumed as 1.

If the value of coded_sub_block_flag is 1 and thus it is determined thata non-zero coefficient exists in the current sub-block, the encodingapparatus may encode sig_coeff_flag having a binary value according to areverse scanning order. The encoding apparatus may encode the 1-bitsyntax element sig_coeff_flag for each transform coefficient accordingto the scanning order. If the value of the transform coefficient at thecurrent scan position is not 0, the value of sig_coeff_flag may be 1.Here, in the case of a subblock including the last non-zero coefficient,sig_coeff_flag does not need to be encoded for the last non-zerocoefficient, so the coding process for the sub-block may be omitted.Level information coding may be performed only when sig_coeff_flag is 1,and four syntax elements may be used in the level information encodingprocess. More specifically, each sig_coeff_flag[xC] [yC] may indicatewhether a level (value) of a corresponding transform coefficient at eachtransform coefficient position (xC, yC) in the current TB is non-zero.In an embodiment, the sig_coeff_flag may correspond to an example of asyntax element of a significant coefficient flag indicating whether aquantized transform coefficient is a non-zero significant coefficient.

A level value remaining after encoding for sig_coeff_flag may be derivedas shown in the following equation. That is, the syntax elementremAbsLevel indicating a level value to be encoded may be derived fromthe following equation.

$\begin{matrix}{{remAbsLevel} = {{{coeff}} - 1}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

Herein, coeff means an actual transform coefficient value.

Additionally, abs_level_gt1_flag may indicate whether or notremAbsLevel′ of the corresponding scanning position (n) is greaterthan 1. For example, when the value of abs_level_gt1_flag is 0, theabsolute value of the transform coefficient of the correspondingposition may be 1. In addition, when the value of the abs_level_gt1_flagis 1, the remAbsLevel indicating the level value to be encoded later maybe updated as shown in the following equation.

$\begin{matrix}{{remAbsLevel} = {{remAbsLevel} - 1}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

In addition, the least significant coefficient (LSB) value ofremAbsLevel described in Equation 2 described above may be encoded as inEquation 3 below through par_level_flag.

$\begin{matrix}{{{par\_ level}{\_ flag}} = {{{{coeff}}\&}1}} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack\end{matrix}$

Herein, par_level_flag[n] may indicate a parity of a transformcoefficient level (value) at a scanning position n.

A transform coefficient level value remAbsLevel that is to be encodedafter performing par_level_flag encoding may be updated as shown belowin the following equation.

$\begin{matrix}{{remAbsLevel} = {{remAbsLevel} ⪢ 1}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

abs_level_gt3_flag may indicate whether or not remAbsLevel′ of thecorresponding scanning position (n) is greater than 3. Encoding forabs_remainder may be performed only in a case where rem_abs_gt3_flag isequal to 1. A relationship between the actual transform coefficientvalue coeff and each syntax element may be as shown below in thefollowing equation.

$\begin{matrix}{{{coeff}} = {{{sig\_ coeff}{\_ flag}} + {{abs\_ level}{\_ gt}\; 1{\_ flag}} + {{par\_ level}{\_ flag}} + {2*\left( {{{abs\_ level}{\_ gt}\; 3{\_ flag}} + {abs\_ remainder}} \right)}}} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack\end{matrix}$

Additionally, the following table indicates examples related to theabove-described Equation 5.

TABLE 5 |coeff[n]| sig_coeff_flag[n] abs_level_gtX_flag[n][0]par_level_flag[n] abs_level_gtX_flag[n][1] abs_remainder[n] 0 0 1 1 0 21 1 0 0 3 1 1 1 0 4 1 1 0 1 0 5 1 1 1 1 0 6 1 1 0 1 1 7 1 1 1 1 1 8 1 10 1 2 9 1 1 1 1 2 10 1 1 0 1 3 11 1 1 1 1 3 . . . . . . . . . . . .

Herein, |coeff| indicates a transform coefficient level (value) and mayalso be indicates as an AbsLevel for a transform coefficient.Additionally, a sign of each coefficient may be encoded by using coeffsign flag, which is a 1-bit symbol.

Also, if the value of the transform skip flag is 1, as shown in Table 4,syntax elements sb_coded_flag, sig_coeff_flag, coeff sign flag,abs_level_gtx_flag, par_level_flag and/or abs_remainder for a residualcoefficient of the transform block may be parsed, and the residualcoefficient may be derived based on the syntax elements. In this case,the syntax elements may be sequentially parsed, and a parsing order maybe changed. In addition, the abs_level_gtx_flag may representabs_level_gt1_flag, abs_level_gt3_flag, abs_level_gt5_flag,abs_level_gt7_flag, and/or abs_level_gt9_flag. For example,abs_level_gtx_flag[n][j] may be a flag indicating whether an absolutevalue or a level (a value) of a transform coefficient at a scanningposition n is greater than (j<<1)+1. The condition (j<<1)+1 may beoptionally replaced with a specific threshold such as a first threshold,a second threshold, or the like.

Meanwhile, CABAC provides high performance, but disadvantageously haspoor throughput performance. This is caused by a regular coding engineof the CABAC. Regular encoding (i.e., coding through the regular codingengine of the CABAC) shows high data dependence since it uses aprobability state and range updated through coding of a previous bin,and it may take a lot of time to read a probability interval anddetermine a current state. The throughput problem of the CABAC may besolved by limiting the number of context-coded bins. For example, asshown in Table 1 or Table 3 described above, a sum of bins used toexpress sig_coeff_flag, abs_level_gt1_flag, par_level_flag, andabs_level_gt3_flag may be limited to the number of bins depending on asize of a corresponding block. Also, for example, as shown in Table 4described above, a sum of bins used to express sig_coeff_flag, coeffsign flag, abs_level_gt1_flag, par_level_flag, abs_level_gt3_flagabs_level_gt5_flag, abs_level_gt7_flag, abs_level_gt9_flag may belimited to the number of bins depending on a size of a correspondingblock. For example, if the corresponding block is a block of a 4×4 size,the sum of bins for the sig_coeff_flag, abs_level_gt1_flag,par_level_flag, abs_level_gt3_flag or sig_coeff_flag, coeff sign flag,abs_level_gt1_flag, par_level_flag, abs_level_gt3_flagabs_level_gt5_flag, abs_level_gt7_flag, abs_level_gt9_flag may belimited to 32 (or ex. 28), and if the corresponding block is a block ofa 2×2 size, the sum of bins for the sig_coeff_flag, abs_level_gt1_flag,par_level_flag, abs_level_gt3_flag may be limited to 8 (or ex. 7). Thelimited number of bins may be represented by remBinsPass1 or RemCcbs.Or, for example, for higher CABAC throughput, the number of contextcoded bins may be limited for a block (CB or TB) including a codingtarget CG. In other words, the number of context coded bins may belimited in units of blocks (CB or TB). For example, when the size of thecurrent block is 16×16, the number of context coded bins for the currentblock may be limited to 1.75 times the number of pixels of the currentblock, i.e., 448, regardless of the current CG.

In this case, if all context-coded bins of which the number is limitedare used when a context element is coded, the encoding apparatus maybinarize the remaining coefficients through a method of binarizing thecoefficient as described below, instead of using the context coding, andmay perform bypass encoding. In other words, for example, if the numberof context-coded bins which are coded for 4×4 CG is 32 (or ex. 28), orif the number of context-coded bins which are coded for 2×2 CG is 8 (orex. 7), sig_coeff_flag, abs_level_gt1_flag, par_level_flag,abs_level_gt3_flag which are coded with the context-coded bin may nolonger be coded, and may be coded directly to dec_abs_level. Or, forexample, when the number of context coded bins coded for a 4×4 block is1.75 times the number of pixels of the entire block, that is, whenlimited to 28, the sig_coeff_flag, abs_level_gt1_flag, par_level_flag,and abs_level_gt3_flag coded as context coded bins may not be coded anymore, and may be directly coded as dec_abs_level as shown in Table 6below.

TABLE 6 |coeff[n]| dec_abs_level[n] 0 0 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 89 9 10 10 11 11 . . . . . .

A value |coeff| may be derived based on dec_abs_level. In this case, atransform coefficient value, i.e., |coeff|, may be derived as shown inthe following equation.

$\begin{matrix}{{{coeff}} = {{dec\_ abs}{\_ level}}} & \left\lbrack {{Equation}\mspace{14mu} 6} \right\rbrack\end{matrix}$

In addition, the coeff_sign_flag may indicate a sign of a transformcoefficient level at a corresponding scanning position n. That is, thecoeff sign flag may indicate the sign of the transform coefficient atthe corresponding scanning position n.

FIG. 8 shows an example of transform coefficients in a 4×4 block.

The 4×4 block of FIG. 8 represents an example of quantized coefficients.The block of FIG. 8 may be a 4×4 transform block, or a 4×4 sub-block ofan 8×8, 16×16, 32×32, or 64×64 transform block. The 4×4 block of FIG. 8may represent a luma block or a chroma block.

Meanwhile, as described above, when an input signal is not a binaryvalue but a syntax element, the encoding apparatus may transform theinput signal into a binary value by binarizing a value of the inputsignal. In addition, the decoding apparatus may decode the syntaxelement to derive a binarized value (e.g., a binarized bin) of thesyntax element, and may de-binarize the binarized value to derive avalue of the syntax element. The binarization process may be performedas a truncated rice (TR) binarization process, a k-th order Exp-Golomb(EGk) binarization process, a limited k-th order Exp-Golomb (limitedEGk), a fixed-length (FL) binarization process, or the like. Inaddition, the de-binarization process may represent a process performedbased on the TR binarization process, the EGk binarization process, orthe FL binarization process to derive the value of the syntax element.

For example, the TR binarization process may be performed as follows.

An input of the TR binarization process may be cMax and cRiceParam for asyntax element and a request for TR binarization. In addition, an outputof the TR binarization process may be TR binarization for symbolValwhich is a value corresponding to a bin string.

Specifically, for example, in the presence of a suffix bin string for asyntax element, a TR bin string for the syntax element may beconcatenation of a prefix bin string and the suffix bin string, and inthe absence of the suffix bin string, the TR bin string for the syntaxelement may be the prefix bin string. For example, the prefix bin stringmay be derived as described below.

A prefix value of the symbolVal for the syntax element may be derived asshown in the following equation.

$\begin{matrix}{{prefixVal} = {{symbolVal} ⪢ {cRiceParam}}} & \left\lbrack {{Equation}\mspace{14mu} 7} \right\rbrack\end{matrix}$

Herein, prefixVal may denote a prefix value of the symbolVal. A prefix(i.e., a prefix bin string) of the TR bin string of the syntax elementmay be derived as described below.

For example, if the prefixVal is less than cMax>>cRiceParam, the prefixbin string may be a bit string of length prefixVal+1, indexed by binIdx.That is, if the prefixVal is less than cMax>>cRiceParam, the prefix binstring may be a bit string of which the number of bits is prefixVal+1,indicated by binIdx. A bin for binIdx less than prefixVal may be equalto 1. In addition, a bin for the same binIdx as the prefixVal may beequal to 0.

For example, a bin string derived through unary binarization for theprefixVal may be as shown in the following table.

TABLE 7 prefixVal Bin string 0 0 1 1 0 2 1 1 0 3 1 1 1 0 4 1 1 1 1 0 5 11 1 1 1 0 . . . binIdx 0 1 2 3 4 5

Meanwhile, if the prefixVal is not less than cMax>>cRiceParam, theprefix bin string may be a bit string in which a length iscMax>>cRiceParam and all bits are 1.

In addition, if cMax is greater than symbolVal and if cRiceParam isgreater than 0, a bin suffix bin string of a TR bin string may bepresent. For example, the suffix bin string may be derived as describedbelow.

A suffix value of the symbolVal for the syntax element may be derived asshown in the following equation.

$\begin{matrix}{{suffixVal} = {{symbolVal} - \left( {({prefixVal}) ⪡ {cRiceParam}} \right)}} & \left\lbrack {{Equation}\mspace{14mu} 8} \right\rbrack\end{matrix}$

Herein, suffixVal may denote a suffix value of the symbolVal.

A suffix of a TR bin string (i.e., a suffix bin string) may be derivedbased on an FL binarization process for suffixVal of which a value cMaxis (1<<cRiceParam)−1.

Meanwhile, if a value of an input parameter, i.e., cRiceParam, is 0, theTR binarization may be precisely truncated unary binarization, and mayalways use the same value cMax as a possible maximum value of a syntaxelement to be decoded.

In addition, for example, the EGk binarization process may be performedas follows. A syntax element coded with ue(v) may be a syntax elementsubjected to Exp-Golomb coding.

For example, a 0-th order Exp-Golomb (EG0) binarization process may beperformed as follows.

A parsing process for the syntax element may begin with reading a bitincluding a first non-zero bit starting at a current position of abitstream and counting the number of leading bits equal to 0. Theprocess may be represented as shown in the following table.

TABLE 8 leadingZeroBits = −1 for( b = 0; !b; leadingZeroBits++ )  b =read_bits( 1 )

In addition, a variable ‘codeNum’ may be derived as shown in thefollowing equation.

$\begin{matrix}{{codeNum} = {2^{leadingZerobits} - 1 + {{read\_ bits}({leadingZeroBits})}}} & \left\lbrack {{Equation}\mspace{14mu} 9} \right\rbrack\end{matrix}$

Herein, a value returned from read_bits(leadingZeroBits), that is, avalue indicated by read_bits(leadingZeroBits), may be interpreted asbinary representation of an unsigned integer for a most significant bitrecorded first.

A structure of an Exp-Golomb code in which a bit string is divided intoa “prefix” bit and a “suffix” bit may be represented as shown in thefollowing table.

TABLE 9 Bit string form Range of codeNum 1 0 0 1 x₀ 1 . . . 2 0 0 1 x₁x₀ 3 . . . 6 0 0 0 1 x₂ x₁ x₀  7 . . . 14 0 0 0 0 1 x₃ x₂ x₁ x₀ 15 . . .30 0 0 0 0 0 1 x₄ x₃ x₂ x₁ x₀ 31 . . . 62 . . . . . .

The “prefix” bit may be a bit parsed as described above to calculateleadingZeroBits, and may be represented by 0 or 1 of a bit string inTable 9. That is, the bit string disclosed by 0 or 1 in Table 9 abovemay represent a prefix bit string. The “suffix” bit may be a bit parsedin the computation of codeNum, and may be represented by xi in Table 9above. That is, a bit string disclosed as xi in Table 9 above mayrepresent a suffix bit string. Herein, i may be a value in the range ofLeadingZeroBits-1. In addition, each xi may be equal to 0 or 1.

A bit string assigned to the codeNum may be as shown in the followingtable.

TABLE 10 Bit string codeNum 1 0 0 1 0 1 0 1 1 2 0 0 1 0 0 3 0 0 1 0 1 40 0 1 1 0 5 0 0 1 1 1 6 0 0 0 1 0 0 0 7 0 0 0 1 0 0 1 8 0 0 0 1 0 1 0 9. . . . . .

If a descriptor of the syntax element is ue(v), that is, if the syntaxelement is coded with ue(v), a value of the syntax element may be equalto codeNum.

In addition, for example, the EGk binarization process may be performedas follows.

An input of the EGk binarization process may be a request for EGkbinarization. In addition, the output of the EGk binarization processmay be EGk binarization for symbolVal, i.e., a value corresponding to abin string.

A bit string of the EGk binarization process for symbolVal may bederived as follows.

TABLE 11 absV = Abs( symbolVal ) stopLoop = 0 do  if( absV >= ( 1 << k )) {   put( 1 )   absV = absV − ( 1 << k )   k++  } else {   put( 0 )  while( k− − )    put( ( absV >> k ) & 1 )   stopLoop = 1  } while(!stopLoop )

Referring to Table 11 above, a binary value X may be added to an end ofa bin string through each call of put(X). Herein, X may be 0 or 1.

In addition, for example, the limited EGk binarization process may beperformed as follows.

An input of the limited EGk binarization process may be a request forlimited EGk binarization, a rice parameter ceParam, log2TranformRange asa variable representing a binary logarithm of a maximum value, andmaxPreExtLen as a variable representing a maximum prefix extensionlength. In addition, an output of the limited EGk binarization processmay be limited EGk binarization for symbolVal as a value correspondingto an empty string.

A bit string of the limited EGk binarization process for the symbolValmay be derived as follows.

TABLE 12 codeValue = symbolVal >> riceParam PrefixExtensionLength = 0while( ( PrefixExtensionLength < maxPrefixExtensionLength ) &&   (codeValue > ( ( 2 << PrefixExtensionLength ) − 2 ) ) ) {  PrefixExtensionLength++   put( 1 )  }  if( PrefixExtensionLength = =maxPrefixExtensionLength )  escapeLength = log2TransformRange  else { escapeLength = PrefixExtensionLength + riceParam  put( 0 )  } symbolVal = symbolVal − ( ( ( 1 << PrefixExtensionLength ) − 1 ) << riceParam )  while( ( escapeLength− − ) > 0 )   put( ( symbolVal >>escapeLength ) & 1 )

In addition, for example, the FL binarization process may be performedas follows.

An input of the FL binarization process may be a request for FLbinarization and cMax for the syntax element. In addition, an output ofthe FL binarization process may be FL binarization for symbolVal as avalue corresponding to a bin string.

FL binarization may be configured by using a bit string of which thenumber of bits has a fixed length of symbolVal. Herein, the fixed-lengthbit may be an unsigned integer bit string. That is, a bit string forsymbolVal as a symbol value may be derived through FL binarization, anda bit length (i.e., the number of bits) of the bit string may be a fixedlength.

For example, the fixed length may be derived as shown in the followingequation.

$\begin{matrix}{{fixedLength} = {{Ceil}\left( {{Log}\; 2\left( {{cMax} + 1} \right)} \right)}} & \left\lbrack {{Equation}\mspace{14mu} 10} \right\rbrack\end{matrix}$

Indexing of bins for FL binarization may be a method using a value whichincreases orderly from a most significant bit to a least significantbit. For example, a bin index related to the most significant bit may bebinIdx=0.

Meanwhile, for example, a binarization process for a syntax elementabs_remainder in the residual information may be performed as follows.

An input of the binarization process for the abs_remainder may be arequest for binarization of a syntax element abs_remainder[n], a colourcomponent cIdx, and a luma position (x0, y0). The luma position (x0, y0)may indicate atop-left sample of a current luma transform block based onthe top-left luma sample of a picture.

An output of the binarization process for the abs_remainder may bebinarization of the abs_remainder (i.e., a binarized bin string of theabs_remainder). Available bin strings for the abs_remainder may bederived through the binarization process.

A rice parameter cRiceParam for the abs_remainder[n] may be derivedthrough a rice parameter derivation process performed by inputting thecolor component cIdx and luma position (x0, y0), the current coefficientscan position (xC, yC), log2TbWidth, which is the binary logarithm ofthe width of the transform block, and log2TbHeight, which is the binarylogarithm of the height of the transform block. A detailed descriptionof the rice parameter derivation process will be described later.

In addition, for example, cMax for abs_remainder[n] to be currentlycoded may be derived based on the rice parameter cRiceParam. The cMaxmay be derived as shown in the following equation.

$\begin{matrix}{{cMax} = {6 ⪡ {cRiceParam}}} & \left\lbrack {{Equation}\mspace{14mu} 11} \right\rbrack\end{matrix}$

Meanwhile, binarization for the abs_remainder, that is, a bin string forthe abs_remainder, may be concatenation of a prefix bin string and asuffix bin string in the presence of the suffix bin string. In addition,in the absence of the suffix bin string, the bin string for theabs_remainder may be the prefix bin string.

For example, the prefix bin string may be derived as described below.

A prefix value prefixVal of the abs_remainder[n] may be derived as shownin the following equation.

$\begin{matrix}{{prefixVal} = {{Min}\left( {{cMax},{{abs\_ remainder}\lbrack n\rbrack}} \right)}} & \left\lbrack {{Equation}\mspace{14mu} 12} \right\rbrack\end{matrix}$

A prefix of the bin string (i.e., a prefix bin string) of theabs_remainder[n] may be derived through a TR binarization process forthe prefixVal, in which the cMax and the cRiceParam are used as aninput.

If the prefix bin string is identical to a bit string in which all bitsare 1 and a bit length is 6, a suffix bin string of the bin string ofthe abs_remainder[n] may exist, and may be derived as described below.

The rice parameter deriving process for the dec_abs_level[n] may be asfollows.

An input of the rice parameter deriving process may be a colourcomponent index cIdx, a luma position (x0, y0), a current coefficientscan position (xC, yC), log2TbWidth as a binary logarithm of a width ofa transform block, and log2TbHeight as a binary logarithm of a height ofthe transform block. The luma position (x0, y0) may indicate atop-leftsample of a current luma transform block based on a top-left luma sampleof a picture. In addition, an output of the rice parameter derivingprocess may be the rice parameter cRiceParam.

For example, a variable locSumAbs may be derived similarly to a pseudocode disclosed in the following table, based on an array AbsLevel[x][y]for a transform block having the given component index cIdx and thetop-left luma position (x0, y0).

TABLE 13 locSumAbs = 0 if( xC < (1 << log2TbWidth) − 1 ) {  locSumAbs +=AbsLevel[ xC + 1 ][ yC ]  if( xC < (1 << log2TbWidth) − 2 )   locSumAbs+= AbsLevel[ xC + 2 ][ yC ]  if( yC < (1 << log2TbHeight) − 1 )  locSumAbs += AbsLevel[ xC + 1 ][ yC + 1 ]     (1532) } if( yC < (1 <<log2TbHeight) − 1 ) {  locSumAbs += AbsLevel[ xC ][ yC + 1 ]  if( yC <(1 << log2TbHeight) − 2 )   locSumAbs += AbsLevel[ xC ][ yC + 2 ] }locSumAbs = Clip3( 0, 31, locSumAbs − baseLevel * 5 )

Then, based on the given variable locSumAbs, the rice parametercRiceParam may be derived as shown in the following table.

TABLE 14 locSumAbs 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 cRiceParam 0 00 0 0 0 0 1 1 1 1 1 1 1 2 2 locSumAbs 16 17 18 19 20 21 22 23 24 25 2627 28 29 30 31 cRiceParam 2 2 2 2 2 2 2 2 2 2 2 2 3 3 3 3

Also, for example, in the rice parameter derivation process forabs_remainder[n], the baseLevel may be set to 4.

Alternatively, for example, the rice parameter cRiceParam may bedetermined based on whether a transform skip is applied to a currentblock. That is, if a transform is not applied to a current TB includinga current CG, in other words, if the transform skip is applied to thecurrent TB including the current CG, the rice parameter cRiceParam maybe derived to be 1.

Also, a suffix value suffixVal of the abs_remainder may be derived asshown in the following equation.

$\begin{matrix}{{suffixVal} = {{{abs\_ remainder}\lbrack n\rbrack} - {cMax}}} & \left\lbrack {{Equation}\mspace{14mu} 13} \right\rbrack\end{matrix}$

A suffix bin string of the bin string of the abs_remainder may bederived through a limited EGk binarization process for the suffixVal inwhich k is set to cRiceParam+1, riceParam is set to cRiceParam, andlog2TransformRange is set to 15, and maxPreExtLen is set to 11.

Meanwhile, for example, a binarization process for a syntax elementdec_abs_level in the residual information may be performed as follows.

An input of the binarization process for the dec_abs_level may be arequest for binarization of a syntax element dec_abs_level[n], a colourcomponent cIdx, a luma position (x0, y0), a current coefficient scanposition (xC, yC), log2TbWidth as a binary logarithm of a width of atransform block, and log2TbHeight as a binary logarithm of a height ofthe transform block. The luma position (x0, y0) may indicate atop-leftsample of a current luma transform block based on a top-left luma sampleof a picture.

An output of the binarization process for the dec_abs_level may bebinarization of the dec_abs_level (i.e., a binarized bin string of thedec_abs_level). Available bin strings for the dec_abs_level may bederived through the binarization process.

A rice parameter cRiceParam for dec_abs_level[n] may be derived througha rice parameter deriving process performed with an input of the colourcomponent cIdx, the luma position (x0, y0), the current coefficient scanposition (xC, yC), the log2TbWidth as the binary logarithm of the widthof the transform block, and the log2TbHeight as the binary logarithm ofthe height of the transform block. The rice parameter deriving processwill be described below in detail.

In addition, for example, cMax for the dec_abs_level[n] may be derivedbased on the rice parameter cRiceParam. The cMax may be derived as shownin the following table.

$\begin{matrix}{{cMax} = {6 ⪡ {cRiceParam}}} & \left\lbrack {{Equation}\mspace{14mu} 14} \right\rbrack\end{matrix}$

Meanwhile, binarization for the dec_abs_level[n], that is, a bin stringfor the dec_abs_level[n], may be concatenation of a prefix bin stringand a suffix bin string in the presence of the suffix bin string. Inaddition, in the absence of the suffix bin string, the bin string forthe dec_abs_level[n] may be the prefix bin string.

For example, the prefix bin string may be derived as described below.

A prefix value prefixVal of the dec_abs_level[n] may be derived as shownin the following equation.

$\begin{matrix}{{prefixVal} = {{Min}\left( {{cMax},{{dec\_ abs}{{\_ level}\lbrack n\rbrack}}} \right)}} & \left\lbrack {{Equation}\mspace{14mu} 15} \right\rbrack\end{matrix}$

A prefix of the bin string (i.e., a prefix bin string) of thedec_abs_level[n] may be derived through a TR binarization process forthe prefixVal, in which the cMax and the cRiceParam are used as aninput.

If the prefix bin string is identical to a bit string in which all bitsare 1 and a bit length is 6, a suffix bin string of the bin string ofthe dec_abs_level[n] may exist, and may be derived as described below.

The rice parameter deriving process for the dec_abs_level[n] may be asfollows.

An input of the rice parameter deriving process may be a colourcomponent index cIdx, a luma position (x0, y0), a current coefficientscan position (xC, yC), log2TbWidth as a binary logarithm of a width ofa transform block, and log2TbHeight as a binary logarithm of a height ofthe transform block. The luma position (x0, y0) may indicate atop-leftsample of a current luma transform block based on a top-left luma sampleof a picture. In addition, an output of the rice parameter derivingprocess may be the rice parameter cRiceParam.

For example, a variable locSumAbs may be derived similarly to a pseudocode disclosed in the following table, based on an array AbsLevel[x][y]for a transform block having the given component index cIdx and thetop-left luma position (x0, y0).

TABLE 15 locSumAbs = 0 if( xC < (1 << log2TbWidth) − 1 ) {  locSumAbs +=AbsLevel[ xC + 1 ][ yC ]  if( xC < (1 << log2TbWidth) − 2 )   locSumAbs+= AbsLevel[ xC + 2 ][ yC ]  if( yC < (1 << log2TbHeight) − 1 )  locSumAbs += AbsLevel[ xC + 1 ][ yC + 1 ]     (1532) } if( yC < (1 <<log2TbHeight) − 1 ) {  locSumAbs += AbsLevel[ xC ][ yC + 1 ]  if( yC <(1 << log2TbHeight) − 2 )   locSumAbs += AbsLevel[ xC ][ yC + 2 ] }locSumAbs = Clip3( 0, 31, locSumAbs − baseLevel * 5 )

Then, based on the given variable locSumAbs, the rice parametercRiceParam may be derived as shown in the following table.

TABLE 16 locSumAbs 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 cRiceParam 0 00 0 0 0 0 1 1 1 1 1 1 1 2 2 locSumAbs 16 17 18 19 20 21 22 23 24 25 2627 28 29 30 31 cRiceParam 2 2 2 2 2 2 2 2 2 2 2 2 3 3 3 3

Also, for example, in the rice parameter derivation process fordec_abs_level[n], the baseLevel may be set to 0, and the ZeroPos[n] maybe derived as follows.

$\begin{matrix}{{{ZeroPos}\lbrack n\rbrack} = {\left( {{{QState} < {2?1}}:2} \right) ⪡ {cRiceParam}}} & \left\lbrack {{Equation}\mspace{14mu} 16} \right\rbrack\end{matrix}$

In addition, a suffix value suffixVal of the dec_abs_level[n] may bederived as shown in the following equation.

$\begin{matrix}{{suffixVal} = {{{dec\_ abs}{{\_ level}\lbrack n\rbrack}} - {cMax}}} & \left\lbrack {{Equation}\mspace{14mu} 17} \right\rbrack\end{matrix}$

A suffix bin string of the bin string of the dec_abs_level[n] may bederived through a limited EGk binarization process for the suffixVal inwhich k is set to cRiceParam+1, truncSuffixLen is set to 15, andmaxPreExtLen is set to 11.

Meanwhile, the RRC and the TSRC may have the following differences.

-   -   For example, in the TSRC, the Rice parameter for the syntax        element abs_remainder[ ] may be derived as 1. The rice parameter        cRiceParam of the syntax element abs_remainder[ ] in the RRC may        be derived based on the lastAbsRemainder and the lastRiceParam        as described above, but the rice parameter cRiceParam of the        syntax element abs_remainder[ ] in the TSRC may be derived as 1.        That is, for example, when transform skip is applied to the        current block (e.g., the current TB), the Rice parameter        cRiceParam for abs_remainder[ ] of the TSRC for the current        block may be derived as 1.    -   Also, for example, referring to Table 3 and Table 4, in the RRC,        abs_level_gtx_flag[n][0] and/or abs_level_gtx_flag[n][1] may be        signaled, but in the TSRC, abs_level_gtx_flag[n][0],        abs_level_gtx_flag[n][1], abs_level_gtx_flag[n][2],        abs_level_gtx_flag[n][3], and abs_level_gtx_flag[n][4] may be        signaled. Here, the abs_level_gtx_flag[n][0] may be expressed as        abs_level_gt1_flag or a first coefficient level flag, the        abs_level_gtx_flag[n][1] may be expressed as abs_level_gt3_flag        or a second coefficient level flag, the abs_level_gtx_flag[n][2]        may be expressed as abs_level_gt5_flag or a third coefficient        level flag, the abs_level_gtx_flag[n][3] may be expressed as        abs_level_gt7_flag or a fourth coefficient level flag, and the        abs_level_gtx_flag[n][4] may be expressed as abs_level_gt9_flag        or a fifth coefficient level flag. Specifically, the first        coefficient level flag may be a flag for whether a coefficient        level is greater than a first threshold (for example, 1), the        second coefficient level flag may be a flag for whether a        coefficient level is greater than a second threshold (for        example, 3), the third coefficient level flag may be a flag for        whether a coefficient level is greater than a third threshold        (for example, 5), the fourth coefficient level flag may be a        flag for whether a coefficient level is greater than a fourth        threshold (for example, 7), the fifth coefficient level flag may        be a flag for whether a coefficient level is greater than a        fifth threshold (for example, 9). As described above, in the        TSRC, compared to the RRC, abs_level_gtx_flag[n][0],        abs_level_gtx_flag[n][1], and abs_level_gtx_flag[n][2],        abs_level_gtx_flag[n][3], abs_level_gtx_flag[n][4] may be        further included.    -   Also, for example, in the RRC, the syntax element coeff sign        flag may be bypass coded, but in the TSRC, the syntax element        coeff_sign_flag may be bypass coded or context coded.

Meanwhile, the present disclosure proposes a method of applying a levelmapping technique in a simplified residual data coding structure for atransform skip block. Here, the transform skip block may represent ablock to which a transform is not applied. In addition, the levelmapping technique may refer to a technique in which an absolutecoefficient level, i.e., absCoeffLevel, is mapped to a modified levelcoded by a method based on a (quantized) left residual sample and a topresidual sample of a current residual sample (i.e., a current residualcoefficient) when block based quantized residual domain differentialpulse-code modulation (BDPCM) is not applied to a current block (eg,CU). The simplified residual data coding structure may be used for onecoding block or the entire transform block or some subblocks/coefficientgroups (CG) under specific conditions such as lossless coding ornear-lossless coding. Alternatively, in the proposed method, the numberof context coded bins that may be used for residual (data) coding withinone TU (Transform Unit, TU) may be limited to a specific threshold, andwhen all of the context coded bins that may be used for the residualcoding of the TU are exhausted (that is, when the number of contextcoded bins for the residual coding of the TU is equal to the specificthreshold), the simplified residual data coding structure may be used.

FIG. 9 illustrates an example of simplified residual data coding for oneCG, transform block, or coding block. With the simplified residualcoding, syntax elements sig_coeff_flag, coeff sign flag, andabs_remainder may be coded. Syntax elements for residual coefficients inthe CG, the transform block, or the coding block may be coded in theorder from top to bottom as shown in FIG. 9. That is, the syntaxelements for a residual coefficient in the CG, the transform block, orthe coding block may be coded in the order of sig_coeff_flag, coeff signflag, and abs_remainder.

The sig_coeff_flag may represent a syntax element for the significantcoefficient flag. The sig_coeff_flag may represent whether a residualcoefficient of a current block (CG, transform block, or coding block) isa non-zero residual coefficient. For example, the sig_coeff_flag mayhave a value of 0 if the value of the residual coefficient of thecorresponding position is 0, and may have a value of 1 if not 0. Also,the coeff sign flag may represent a syntax element for a sign flag ofthe residual coefficient. The sig_coeff_flag may represent a sign of theresidual coefficient. For example, the coeff sign flag may mean a signvalue of a residual coefficient of a corresponding position. There maybe various methods for applying the coeff_sign_flag. For example, whenthe residual coefficient of the corresponding position is 0, that is,when the value of sig_coeff_flag for the residual coefficient is 0, thecoeff sign flag may not be coded. And, for non-zero residualcoefficients, the coeff sign flag may have a value of 1 (or 0) when theresidual coefficient of the corresponding position is a negative value,and the coeff sign flag may have a value of 0 (or 1) when the residualcoefficient of the corresponding position is a positive value.Alternatively, regardless of the value of sig_coeff_flag of the residualcoefficient, when the residual coefficient is a negative value, thecoeff sign flag may have a value of 1 (or 0), and when the residualcoefficient is a positive value or 0, the coeff sign flag may have avalue of 0 (or 1). Alternatively, when the residual coefficient is apositive value, the coeff sign flag may have a value of 1 (or 0), andwhen the residual coefficient is a negative value or 0, thecoeff_sign_flag may have a value of 0 (or 1). Also, the abs_remaindermay represent a syntax element for residual level value information orcoefficient value related information. For example, the abs_remaindermay mean a residual level value. For example, when the value ofsig_coeff_flag for the residual coefficient is 0, the abs_remainder forthe residual coefficient may not be coded, when the value ofsig_coeff_flag for the residual coefficient is 1, the abs_remainder mayhave a value obtained by subtracting 1 from the absolute value of theresidual coefficient (absolute value−1).

Meanwhile, even when the regular residual coding is performed, if aspecific condition is satisfied, it may be converted into the simplifiedresidual data coding shown in FIG. 9. For example, the specificcondition may be a case in which all of the context coded bins that canbe used are exhausted when the residual information of the correspondingcoding block is lossless or near lossless coded and/or when a TU levelcontext coded bin constraint algorithm is applied.

FIG. 10 illustrates another example of simplified residual data codingfor one CG, transform block, or coding block. With the simplifiedresidual coding, syntax elements dec_abs_level, coeff_sign_flag may becoded. Syntax elements for residual coefficients in the CG, thetransform block, or the coding block may be coded in the order from topto bottom as shown in FIG. 10. That is, the syntax elements for aresidual coefficient in the CG, the transform block, or the coding blockmay be coded in the order of dec_abs_level, coeff_sign_flag.

Referring to FIG. 10, the dec_abs_level may represent a syntax elementfor coefficient value related information, and the coeff_sign_flag mayrepresent a syntax element for a sign flag of the residual coefficient.For example, according to the structure shown in FIG. 10, when theresidual coefficient is 0, a value of the dec_abs_level may be 0, andwhen the residual coefficient is not 0, the value of the dec_abs_levelmay be an absolute value of the residual coefficient. Also, for example,the coeff sign flag may mean a sign value of a residual coefficient of acorresponding position. There may be various methods for applying thecoeff sign flag. For example, when the residual coefficient of thecorresponding position is 0, the coeff_sign_flag may not be coded. And,for non-zero residual coefficients, the coeff sign flag may have a valueof 1 (or 0) when the residual coefficient of the corresponding positionis a negative value, and the coeff_sign_flag may have a value of 0(or 1) when the residual coefficient of the corresponding position is apositive value. Alternatively, the coeff sign flag may be codedregardless of dec_abs_level of the residual coefficient, when theresidual coefficient is a negative value, the coeff_sign_flag may have avalue of 1 (or 0), and when the residual coefficient is a positive valueor 0, the coeff_sign_flag may have a value of 0 (or 1). Alternatively,when the residual coefficient is a positive value, the coeff_sign_flagmay have a value of 1 (or 0), and when the residual coefficient is anegative value or 0, the coeff sign flag may have a value of 0 (or 1).

Meanwhile, even when the regular residual coding is performed, if aspecific condition is satisfied, it may be converted into the simplifiedresidual data coding shown in FIG. 10. For example, the specificcondition may be a case in which all of the context coded bins that canbe used are exhausted when the residual information of the correspondingcoding block is lossless or near lossless coded and/or when a TU levelcontext coded bin constraint algorithm is applied.

FIG. 11 illustrates another example of simplified residual data codingfor one CG, transform block, or coding block. With the simplifiedresidual coding, syntax elements coeff sign flag, dec_abs_level may becoded. Syntax elements for residual coefficients in the CG, thetransform block, or the coding block may be coded in the order from topto bottom as shown in FIG. 11. That is, the syntax elements for aresidual coefficient in the CG, the transform block, or the coding blockmay be coded in the order of coeff_sign_flag, dec_abs_level.

Referring to FIG. 11, the the coeff_sign_flag may represent a syntaxelement for a sign flag of the residual coefficient, and thedec_abs_level may represent a syntax element for coefficient valuerelated information. For example, when the residual coefficient of theposition to be coded is a negative value, the coeff sign flag may have avalue of 1 (or 0), and when the residual coefficient is a positive valueor 0, the coeff_sign_flag may have a value of 0 (or 1). Alternatively,for example, when the residual coefficient is a positive value, thecoeff sign flag may have a value of 1 (or 0), and when the residualcoefficient is a negative value or 0, the coeff_sign_flag may have avalue of 0 (or 1).

Meanwhile, even when the regular residual coding is performed, if aspecific condition is satisfied, it may be converted into the simplifiedresidual data coding shown in FIG. 11. For example, the specificcondition may be a case in which all of the context coded bins that canbe used are exhausted when the residual information of the correspondingcoding block is lossless or near lossless coded and/or when a TU levelcontext coded bin constraint algorithm is applied.

Meanwhile, as described above, the level mapping technique for thetransform skip mode may be used. For example, in the level mappingtechnique, a value of abs_level_gtx_flag[0] may be used as a valuerepresenting whether level mapping is performed. That is, whether to mapthe level may be determined based on the value of theabs_level_gtx_flag[0]. Accordingly, in the simplified residual datacoding structure in which abs_level_gtx_flag[0] is not coded, decodingof residual coefficients to which level mapping is applied cannot beproperly performed. Accordingly, the present disclosure proposes amethod not to use level mapping for a coding block, a transform block, acoefficient group, and/or a residual coefficient to which simplifiedresidual data coding is applied so that the simplified residual datacoding structure of FIG. 9, FIG. 10 or FIG. 11 and level mapping can beused together. According to an embodiment of the present disclosure, thesimplified residual data coding structure and level mapping can becombined without problems in residual coding for a transform skip block.

For example, in one coding block, the residual data coding method forthe transform skip block shown in Table 4 and the simplified residualdata coding method may be mixed, when the residual data coding for thetransform skip block is applied, the level mapping technique shown inTable 4 may be applied as it is, and when the simplified residual datacoding is applied, the level mapping technique may be applied.

Table 17 and Table 18 to be described below exemplarily show syntax towhich an embodiment proposed in the present disclosure is applied.

TABLE 17 Descriptor residual_ts_coding( x0, y0, log2TbWidth,log2TbHeight, cIdx ) { ...    if( intra_bdpcm_flag = = 0 | | (MaxCcbs >0) | | ((MaxCcbs <= 0) && abs_level_gtx_flag[n][0])){     absRightCoeff= abs( TransCoeffLevel[ x0 ][ y0 ][ cIdx ][ xC − 1 ][ yC ] )    absBelowCoeff = abs( TransCoeffLevel[ x0 ][ y0 ][ cIdx ][ xC ][ yC −1 ] )     predCoeff = Max( absRightCoeff, absBelowCoeff )     if(AbsLevelPassX[ xC ][ yC ] + abs_remainder[ n ] = = 1 && predCoeff > 0 )     TransCoeffLevel[ x0 ][ y0 ][ cIdx ][ xC ][ yC ] =       ( 1 − 2 *coeff_sign_flag[ n ] ) * predCoeff     else if( AbsLevelPassX[ xC ][ yC] + abs_remainder[ n ] <= predCoeff )      TransCoeffLevel[ x0 ][ y0 ][cIdx ][ xC ][ yC ] = ( 1 − 2 * coeff_sign_flag[ n ] ) *       (AbsLevelPassX[ xC ][ yC ] + abs_remainder[ n ] − 1)     else     TransCoeffLevel[ x0 ][ y0 ][ cIdx ][ xC ][ yC ] = ( 1 − 2 *coeff_sign_flag[ n ] ) *       ( AbsLevelPassX[ xC ][ yC ] +abs_remainder[ n ] )    } else     TransCoeffLevel[ x0 ][ y0 ][ cIdx ][xC ][ yC ] = ( 1 − 2 * coeff_sign_flag[ n ] ) *       ( AbsLevelPassX[xC ][ yC ] + abs_remainder[ n ] )   }  } }

TABLE 18 Descriptor residual_ts_coding( x0, y0, log2TbWidth,log2TbHeight, cIdx ) { ...    if( intra_bdpcm_flag = = 0 | |tranquant_bypass_flag == 0){     absRightCoeff = abs( TransCoeffLevel[x0 ][ y0 ][ cIdx ][ xC − 1 ][ yC ] )     absBelowCoeff = abs(TransCoeffLevel[ x0 ][ y0 ][ cIdx ][ xC ][ yC − 1 ] )     predCoeff =Max( absRightCoeff, absBelowCoeff )     if( AbsLevelPassX[ xC ][ yC ] +abs_remainder[ n ] = = 1 && predCoeff > 0 )      TransCoeffLevel[ x0 ][y0 ][ cIdx ][ xC ][ yC ] =       ( 1 − 2 * coeff_sign_flag[ n ] ) *predCoeff     else if( AbsLevelPassX[ xC ][ yC ] + abs_remainder[ n ] <=predCoeff )      TransCoeffLevel[ x0 ][ y0 ][ cIdx ][ xC ][ yC ] = ( 1 −2 * coeff_sign_flag[ n ] ) *       ( AbsLevelPassX[ xC ][ yC ] +abs_remainder[ n ] − 1)     else      TransCoeffLevel[ x0 ][ y0 ][ cIdx][ xC ][ yC ] = ( 1 − 2 * coeff_sign_flag[ n ] ) *       (AbsLevelPassX[ xC ][ yC ] + abs_remainder[ n ] )    } else    TransCoeflLevel[ x0 ][ y0 ][ cIdx ][ xC ][ yC ] = ( 1 − 2 *coeff_sign_flag[ n ] ) *       ( AbsLevelPassX[ xC ][ yC ] +abs_remainder[ n ] )   }  } }

Table 17 may represent a syntax structure that prevents level mappingfrom being performed when the context coded bin constraint algorithm isapplied, the available context coded bins (MaxCcbs represents the numberof context coded bins that can be used) are exhausted and converted intothe simplified residual data coding structure. In addition, Table 18 mayrepresent a syntax structure to which the method proposed in the presentdisclosure is applied when a simplified residual data coding structureis used for a lossless coding block. Here, for example,transquant_bypass_flag shown in Table 18 may be a syntax elementrepresenting whether lossless coding is applied. Thetransquant_bypass_flag may be signaled at the CU or TU or picture level.

Meanwhile, Table 17 and Table 18 are only examples to which anembodiment proposed in the present disclosure is applied, and are notlimited thereto. In the present disclosure, as an embodiment, when thesimplified residual data coding structure is performed, in order toencode/decode the level-mapped residual coefficient, it is proposed thata process of correcting the encoded/decoded level is not performed. Thatis, for example, a method of deriving the residual coefficients of thecurrent block using a simplified residual data coding structure withoutderiving the residual coefficients through level mapping when all thecontext coded bins for the current block are used may be proposed. Thesimplified residual data coding structure may be as described above. Forexample, when all of the context coded bins for the current block areused, the residual coefficient may be derived based on a value ofinformation representing an absolute value and sign information. Also,for example, Table 4 may represent an example to which the embodimentproposed in the present disclosure is applied.

FIG. 12 briefly illustrates an image encoding method performed by anencoding apparatus according to the present disclosure. The methoddisclosed in FIG. 12 may be performed by the encoding apparatusdisclosed in FIG. 2. Specifically, for example, S1200 of FIG. 12 may beperformed by a predictor of the encoding apparatus; S1210 to S1220 ofFIG. 12 may be performed by a residual processor of the encodingapparatus; and S1230 may be performed by an entropy encoder of theencoding apparatus. Also, although not shown, a process of generating areconstructed picture and a reconstructed sample for the current blockbased on a predicted sample and a residual sample for the current blockmay be performed by an adder of the encoding apparatus.

The encoding apparatus derives a prediction sample of a current blockbased on inter prediction or intra prediction (S1200). The encodingapparatus may derive prediction samples of the current block based onthe prediction mode. In this case, various prediction methods disclosedin this document, such as inter prediction or intra prediction, may beapplied.

For example, the encoding apparatus may determine whether to performinter prediction or intra prediction on a current block, and maydetermine specific inter prediction mode or specific intra predictionmode based on RD cost. According to the determined mode, the encodingapparatus may derive the prediction sample for the current block.

The encoding apparatus derives a residual sample of the current blockbased on the prediction sample (S1210). For example, the encodingapparatus may derive the residual sample through the subtraction of theoriginal sample and the prediction sample for the current block.

The encoding apparatus derives a current residual coefficient based onthe residual sample (S1220). For example, the encoding apparatus mayderive a current residual coefficient of the current block based on theresidual sample. For example, the encoding apparatus may determinewhether transform is applied to the current block. That is, the encodingapparatus may determine whether transform is applied to the residualsample of the current block. The encoding apparatus may determinewhether or not to apply the transform to the current block inconsideration of coding efficiency. For example, the encoding apparatusmay determine that transform is not applied to the current block. Ablock to which the transform is not applied may be referred to as atransform skip block. That is, for example, the current block may be atransform skip block.

If the transform is not applied to the current block, that is, if thetransform is not applied to the residual sample, the encoding apparatusmay derive the derived residual sample as the current residualcoefficient. In addition, if the transform is applied to the currentblock, that is, if the transform is applied to the residual sample, theencoding apparatus may derive the current residual coefficient byperforming the transform on the residual sample. The current residualcoefficient may be included in a current sub-block of the current block.The current sub-block may be called a current coefficient group (CG). Inaddition, the size of the current sub-block of the current block may bea 4×4 size or a 2×2 size. That is, the current sub-block of the currentblock may include up to 16 non-zero residual coefficients or up to 4non-zero residual coefficients.

Here, the current block may be a coding block (CB) or a transform block(TB). Also, the residual coefficient may be referred to as a transformcoefficient.

Meanwhile, for example, the current residual coefficient may be derivedwithout performing level mapping. For example, a number of context-codedresidual syntax elements for residual coefficients prior to the currentresidual coefficient among residual coefficients of the current blockmay be equal to a maximum number of context coded bins of the currentblock, and the residual syntax elements for the current residualcoefficient may include absolute level information for the currentresidual coefficient and a sign flag of the residual coefficient, andthe current residual coefficient may be derived without performing levelmapping. Here, deriving the current residual coefficient using only theabsolute level information and the sign flag may be represented assimplified residual data coding. That is, the residual coefficients maybe derived based on simplified residual data coding. Additionally, forexample, context coded bins for the current block may be all used asbins of context-coded residual syntax elements for residual coefficientsprior to the current residual coefficient among residual coefficients ofthe current block, and the residual syntax elements for the currentresidual coefficient may include coefficient level information for thecurrent residual coefficient and a sign flag of the residualcoefficient, and the current residual coefficient may be derived withoutperforming level mapping. For example, when all of the maximum number ofcontext coded bins for the current block are used for residual syntaxelements for previous residual coefficients of the current residualcoefficient in the scanning order, and the residual syntax elements forthe current residual coefficient may include coefficient levelinformation for the current residual coefficient and a sign flag of theresidual coefficient, and the current residual coefficient may bederived without performing level mapping. Also, for example, theresidual coefficients prior to the current residual coefficient may bederived by performing the level mapping.

Meanwhile, for example, the level mapping may represent a method shownin Table 19.

TABLE 19  pred = max(X0, X1);   if (absCoeff = = pred)   {   absCoeffMod = 1;   }   else   {    absCoeffMod = (absCoeff < pred) ?absCoeff + 1 : absCoeff; }

Here, Xo may represent a left absolute coefficient level of the currentresidual coefficient (that is, a coefficient level of the left residualsample (left residual coefficient)), Xi may represent a top absolutecoefficient level of the current residual coefficient (that is, acoefficient level of the top residual sample (top residualcoefficient)). Also, absCoeff may represent the absolute levelcoefficient of the current residual coefficient, and absCoeffMod mayrepresent the level mapped level through the above-described process.

For example, the level mapping may mean a process of deriving a minimumvalue among an absolute level of the left residual coefficient of aresidual coefficient and an absolute level of the top residualcoefficient of the residual coefficient, modifying an absolute level ofthe residual coefficient based on the minimum value by comparing theminimum value and the absolute level of the residual coefficient.

The encoding apparatus encodes image information including predictionmode information representing a prediction mode of the current block andresidual syntax elements for the current residual coefficient (S1230).The encoding apparatus may encode image information including predictionmode information representing a prediction mode of the current block andresidual syntax elements for the current residual coefficient. Forexample, the encoding apparatus may generate and encode predictionrelated information for the current block. The prediction relatedinformation may include the prediction mode information. Additionally,the encoding apparatus may encode residual information includingresidual syntax elements for the current residual coefficient of thecurrent block. The image information may include the residualinformation. For example, the encoding apparatus may encode imageinformation including the residual information, and output the encodedimage information in the form of a bitstream. The bitstream may betransmitted to the decoding apparatus through a network or a storagemedium.

Also, for example, a number of context-coded residual syntax elementsfor residual coefficients prior to the current residual coefficientamong residual coefficients of the current block may be equal to amaximum number of context coded bins of the current block. That is, forexample, the context coded bins for the current block may be all used asbins of context-coded residual syntax elements for residual coefficientsprior to the current residual coefficient among residual coefficients ofthe current block. In other words, for example, all of the maximumnumber of context coded bins for the current block may be used forresidual syntax elements for previous residual coefficients of thecurrent residual coefficient in the scanning order. Meanwhile, forexample, the maximum number of context coded bins of the current blockmay be derived based on a width and a height of the current block.

For example, a number of context-coded residual syntax elements forresidual coefficients prior to the current residual coefficient amongresidual coefficients of the current block may be equal to a maximumnumber of context coded bins of the current block, residual syntaxelements for the current residual coefficient may include absolute levelinformation for the current residual coefficient and a sign flag of thecurrent residual coefficient. For example, the context coded bins forthe current block may be all used as bins of context-coded residualsyntax elements for residual coefficients prior to the current residualcoefficient among residual coefficients of the current block, residualsyntax elements for the current residual coefficient may includecoefficient level information for the current residual coefficient and asign flag of the current residual coefficient. For example, when all ofthe maximum number of context coded bins for the current block are usedfor residual syntax elements for previous residual coefficients of thecurrent residual coefficient in the scanning order, residual syntaxelements for the current residual coefficient may include coefficientlevel information for the current residual coefficient and a sign flagof the current residual coefficient. The residual syntax elements forthe current residual coefficient be encoded based on bypass. That is,the residual syntax elements for the current residual coefficient may beencoded based on a uniform probability distribution. For example, thecoefficient level information may represent an absolute value of thecoefficient level of the current residual coefficient. Also, the signflag may represent a sign of the current residual coefficient. Forexample, when a value of the sign flag is 0, the sign flag may representthat the coefficient level of the current residual coefficient is apositive value, when the value of the sign flag is 1, the sign flag mayrepresent that the coefficient level of the current residual coefficientis a negative value. The coefficient level information may be theabs_remainder, and the sign flag may be the coeff sign flag.

Also, for example, the residual information may include a transform skipflag for the current block. The transform skip flag may representwhether transform is applied to the current block. That is, thetransform skip flag may represent whether transform is applied to theresidual coefficients of the current block. The syntax elementrepresenting the transform skip flag may be the transform_skip_flag. Forexample, when a value of the transform skip flag is 0, the transformskip flag may represent that transform is not applied to the currentblock, when a value of the transform skip flag is 1, the transform skipflag may represent that transform is applied to the current block. Forexample, when the current block is a transform skip block, the value ofthe transform skip flag for the current block may be 1.

Also, for example, the encoding apparatus may generate the residualinformation of the current block based on residual samples of thecurrent block. For example, the image information may include theresidual information for the current block. For example, the residualinformation may include residual syntax elements for a residualcoefficient before the current residual coefficient in a scanning order.For example, the residual syntax elements may include syntax elementssuch as coded_sub_block_flag, sig_coeff_flag, coeff sign flag,abs_level_gt1_flag, par_level_flag, abs_level_gtX_flag, abs_remainderand/or coeff_sign_flag.

For example, the context-coded residual syntax elements may include asignificant coefficient flag representing whether the residualcoefficient is a non-zero residual coefficient, a parity level flag fora parity of the coefficient level for the residual coefficient, a signflag representing a sign for the residual coefficient, a firstcoefficient level flag for whether the coefficient level is greater thana first threshold and/or a second coefficient level flag for whether thecoefficient level is greater than a second threshold. Also, for example,the context-coded residual syntax elements may include a thirdcoefficient level flag for whether the coefficient level is greater thana third threshold, a fourth coefficient level flag for whether thecoefficient level of the residual coefficient is greater than a fourththreshold and/or a fifth coefficient level flag for whether thecoefficient level of the residual coefficient is greater than a fifththreshold. Here, the significant coefficient flag may be sig_coeff_flag,the parity level flag may be par_level_flag, the sign flag may be coeffsign flag, the first coefficient level flag may be abs_level_gt1_flag,the second coefficient level flag may be abs_level_gt3_flag orabs_level_gtx_flag. Also, the third coefficient level flag may beabs_level_gt5_flag or abs_level_gtx_flag, the fourth coefficient levelflag may be abs_level_gt7_flag or abs_level_gtx_flag, the fifthcoefficient level flag may be abs_level_gt9_flag or abs_level_gtx_flag.

Also, for example, the residual information may include a bypass basedcoded syntax element for a residual coefficient of the current block.The bypass coded syntax element may include coefficient levelinformation on a value of the current residual coefficient. Thecoefficient level information may be abs_remainder or dec_abs_level.Also, the bypass coded syntax element may include the sign flag.

Also, for example, the encoding apparatus may generate predictioninformation for the current block. The image information may include theprediction information for the current block. The prediction informationmay include information for an inter prediction mode or an intraprediction mode performed on the current block. The decoding apparatusmay perform inter prediction or intra prediction on the current blockbased on the prediction information received through the bitstream, andmay derive prediction samples of the current block.

Meanwhile, the bitstream may be transmitted to the decoding apparatusthrough over a network or a (digital) storage medium. Here, the networkmay include a broadcasting network and/or a communication network, andthe digital storage medium may include various storage media such asUSB, SD, CD, DVD, Blu-ray, HDD, SSD, and the like.

FIG. 13 briefly illustrates an encoding apparatus for performing animage encoding method according to the present disclosure. The methoddisclosed in FIG. 12 may be performed by the encoding apparatusdisclosed in FIG. 13. Specifically, for example, the predictor of theencoding apparatus of FIG. 13 may perform steps S1200 of FIG. 12; theresidual processor of the encoding apparatus of FIG. 13 may performS1210 to S1220 of FIG. 12; and the entropy encoder of the encodingapparatus of FIG. 13 may perform S1230 of FIG. 12. Also, although notshown, a process of generating a reconstructed picture and areconstructed sample for the current block based on a predicted sampleand a residual sample for the current block may be performed by an adderof the encoding apparatus.

FIG. 14 briefly illustrates an image decoding method performed by adecoding apparatus according to the present disclosure. The methoddisclosed in FIG. 14 may be performed by the decoding apparatusdisclosed in FIG. 3. Specifically, for example, S1400 of FIG. 14 may beperformed by the entropy decoder of the decoding apparatus; S1410 toS1420 may be performed by the predictor of the decoding apparatus; S1430to S1440 may be performed by the residual processor of the decodingapparatus; and S1450 may be performed by an adder of the decodingapparatus.

The decoding apparatus obtains image information including predictionmode information and residual information through a bitstream (S1400).The decoding apparatus may obtain image information including predictionmode information and residual information for the current block througha bitstream. For example, the image information may include predictionmode information for the current block. For example, the imageinformation may include prediction related information for the currentblock, and the prediction related information may include the predictionmode information. The prediction mode information may indicate whetherinter prediction or intra prediction is applied to the current block.

Also, for example, the residual information may include residual syntaxelements for a current residual coefficient in a current block. Also,for example, the residual information may include residual syntaxelements for residual coefficients in the current block. Here, thecurrent block may be a coding block (CB) or a transform block (TB). Inaddition, the residual coefficient may be referred to as a transformcoefficient.

Also, for example, the current block may be a transform skip block.

Also, for example, a number of context-coded residual syntax elementsfor residual coefficients prior to the current residual coefficientamong residual coefficients of the current block may be equal to amaximum number of context coded bins of the current block, residualsyntax elements for the current residual coefficient may includeabsolute level information for the current residual coefficient and asign flag of the current residual coefficient. The maximum number ofcontext coded bins of the current block may be derived based on a widthand a height of the current block. For example, the maximum contextcoded bins for the current block may be all used as bins ofcontext-coded residual syntax elements for residual coefficients priorto the current residual coefficient among residual coefficients of thecurrent block, residual syntax elements for the current residualcoefficient may include coefficient level information for the currentresidual coefficient and a sign flag of the current residualcoefficient. For example, when all of the maximum number of contextcoded bins for the current block are used for residual syntax elementsfor previous residual coefficients of the current residual coefficientin the scanning order, residual syntax elements for the current residualcoefficient may include coefficient level information for the currentresidual coefficient and a sign flag of the current residualcoefficient. The residual syntax elements for the current residualcoefficient be decoded based on bypass. That is, the residual syntaxelements for the current residual coefficient may be decoded based on auniform probability distribution. For example, the coefficient levelinformation may represent an absolute value of the coefficient level ofthe current residual coefficient. Also, the sign flag may represent asign of the current residual coefficient. For example, when a value ofthe sign flag is 0, the sign flag may represent that the coefficientlevel of the current residual coefficient is a positive value, when thevalue of the sign flag is 1, the sign flag may represent that thecoefficient level of the current residual coefficient is a negativevalue. The coefficient level information may be the abs_remainder, andthe sign flag may be the coeff sign flag.

Also, for example, the residual information may include a transform skipflag for the current block. The transform skip flag may representwhether transform is applied to the current block. That is, thetransform skip flag may represent whether transform is applied to theresidual coefficients of the current block. The syntax elementrepresenting the transform skip flag may be the transform_skip_flag. Forexample, when a value of the transform skip flag is 0, the transformskip flag may represent that transform is not applied to the currentblock, when a value of the transform skip flag is 1, the transform skipflag may represent that transform is applied to the current block. Forexample, when the current block is a transform skip block, the value ofthe transform skip flag for the current block may be 1.

Also, for example, the image information may include the residualinformation for the current block. For example, the residual informationmay include residual syntax elements for a residual coefficient beforethe current residual coefficient in a scanning order. For example, theresidual syntax elements may include syntax elements such ascoded_sub_block_flag, sig_coeff_flag, coeff sign flag,abs_level_gt1_flag, par_level_flag, abs_level_gtX_flag, abs_remainderand/or coeff sign flag.

For example, the context-coded residual syntax elements may include asignificant coefficient flag representing whether the residualcoefficient is a non-zero residual coefficient, a parity level flag fora parity of the coefficient level for the residual coefficient, a signflag representing a sign for the residual coefficient, a firstcoefficient level flag for whether the coefficient level is greater thana first threshold and/or a second coefficient level flag for whether thecoefficient level is greater than a second threshold. Also, for example,the context-coded residual syntax elements may include a thirdcoefficient level flag for whether the coefficient level is greater thana third threshold, a fourth coefficient level flag for whether thecoefficient level of the residual coefficient is greater than a fourththreshold and/or a fifth coefficient level flag for whether thecoefficient level of the residual coefficient is greater than a fifththreshold. Here, the significant coefficient flag may be sig_coeff_flag,the parity level flag may be par_level_flag, the sign flag may be coeffsign flag, the first coefficient level flag may be abs_level_gt1_flag,the second coefficient level flag may be abs_level_gt3_flag orabs_level_gtx_flag. Also, the third coefficient level flag may beabs_level_gt5_flag or abs_level_gtx_flag, the fourth coefficient levelflag may be abs_level_gt7_flag or abs_level_gtx_flag, the fifthcoefficient level flag may be abs_level_gt9_flag or abs_level_gtx_flag.

Also, for example, the residual information may include a bypass basedcoded syntax element for a residual coefficient of the current block.The bypass coded syntax element may include coefficient levelinformation on a value of the current residual coefficient. Thecoefficient level information may be abs_remainder or dec_abs_level.Also, the bypass coded syntax element may include the sign flag.

The decoding apparatus derives a prediction mode of a current blockbased on the prediction mode information (S1410). The decoding apparatusmay determine whether inter prediction or intra prediction is applied tothe current block based on the prediction mode information, and mayperform prediction based on this.

The decoding apparatus derives a prediction sample based on theprediction mode (S1420).

For example, the decoding apparatus may derive a prediction mode appliedto the current block based on the prediction mode information, and mayderive a prediction sample of the current block based on the predictionmode. For example, when inter prediction is applied to the currentblock, the decoding apparatus may derive motion information of thecurrent block based on the prediction related information included inthe image information, and may derive the prediction sample of thecurrent block based on the motion information. Additionally, forexample, when intra prediction is applied to the current block, thedecoding apparatus may derive a reference sample based on neighboringsamples of the current block, and may derive the prediction sample ofthe current block based on the reference sample and the intra predictionmode of the current block. The reference samples may include upperreference samples and left reference samples of the current block. Forexample, when a size of the current block is N×N, and an x component ofa top-left sample position of the current block is 0, and a y componentthereof is 0, then the left reference samples may be p[−1][0] top[−1][2N−1], the top reference samples may be p[0][−1] to p[2N−1][−1].

The decoding apparatus derives a current residual coefficient based onresidual syntax elements for the current residual coefficient in thecurrent block (S1430). The decoding apparatus may derive the currentresidual coefficient based on the residual syntax elements. The residualsyntax elements may include coefficient level information for thecurrent residual coefficient and a sign flag of the residualcoefficient.

For example, an absolute level of the current residual coefficient maybe derived as a value indicated by coefficient level information for thecurrent residual coefficient, and a sign of the current residualcoefficient may be derived as a sign indicated by the sign flag.

Meanwhile, for example, the current residual coefficient may be derivedwithout performing level mapping. For example, a number of context-codedresidual syntax elements for residual coefficients prior to the currentresidual coefficient among residual coefficients of the current blockmay be equal to a maximum number of context coded bins of the currentblock, and the residual syntax elements for the current residualcoefficient may include absolute level information for the currentresidual coefficient and a sign flag of the residual coefficient, andthe current residual coefficient may be derived without performing levelmapping. Here, deriving the current residual coefficient using only theabsolute level information and the sign flag may be represented assimplified residual data coding. That is, the residual coefficients maybe derived based on simplified residual data coding. Additionally, forexample, context coded bins for the current block may be all used asbins of context-coded residual syntax elements for residual coefficientsprior to the current residual coefficient among residual coefficients ofthe current block, and the residual syntax elements for the currentresidual coefficient may include coefficient level information for thecurrent residual coefficient and a sign flag of the residualcoefficient, and the current residual coefficient may be derived withoutperforming level mapping. For example, when all of the maximum number ofcontext coded bins for the current block are used for residual syntaxelements for previous residual coefficients of the current residualcoefficient in the scanning order, the residual syntax elements for thecurrent residual coefficient may include coefficient level informationfor the current residual coefficient and a sign flag of the residualcoefficient, and the current residual coefficient may be derived withoutperforming level mapping. Also, for example, the residual coefficientsprior to the current residual coefficient may be derived by performingthe level mapping.

Meanwhile, for example, the level mapping may represent the method shownin Table 19 described above. For example, the level mapping may mean aprocess of deriving a minimum value among an absolute level of the leftresidual coefficient of a residual coefficient and an absolute level ofthe top residual coefficient of the residual coefficient, modifying anabsolute level of the residual coefficient based on the minimum value bycomparing the minimum value and the absolute level of the residualcoefficient.

The decoding apparatus derives a residual sample based on the currentresidual coefficient (S1440). The decoding apparatus may derive theresidual sample of the current block based on the current residualcoefficient. That is, the decoding apparatus may derive the residualsample of the current block based on the current residual coefficient.For example, when it is derived that transform is not applied to thecurrent block based on the transform skip flag, that is, when the valueof the transform skip flag is one (1), the decoding apparatus may derivethe current residual coefficient as the residual sample of the currentblock. Alternatively, for example, when it is derived that transform isnot applied to the current block based on the transform skip flag, thatis, when the value of the transform skip flag is 1, the decodingapparatus may derive the residual sample of the current block bydequantizing the current residual coefficient. Alternatively, forexample, when it is derived that transform is applied to the currentblock based on the transform skip flag, that is, when the value of thetransform skip flag is zero (0), the decoding apparatus may derive theresidual sample of the current block by inverse transforming the currentresidual coefficient. Alternatively, for example, when it is derivedthat transform is applied to the current block based on the transformskip flag, that is, when the value of the transform skip flag is 0, thedecoding apparatus may derive the residual sample of the current blockby dequantizing the current residual coefficient and inversetransforming the dequantized coefficient.

The decoding apparatus derive a reconstructed sample of the currentblock based on the residual sample and the prediction sample (S1450).

For example, the decoding apparatus may derive a reconstructed sample ofthe current block based on the residual sample and the predictionsample. For example, the decoding apparatus may generate thereconstructed sample through addition of the prediction sample and theresidual sample.

Thereafter, optionally, an in-loop filtering procedure such asdeblocking filtering, SAO, and/or ALF procedures may be applied to thereconstructed picture as described above in order to improvesubjective/objective picture quality.

FIG. 15 schematically represents a decoding apparatus for performing animage decoding method according to the document. The method disclosed inFIG. 14 may be performed by the decoding apparatus disclosed in FIG. 15.Specifically, for example, the entropy decoder of the decoding apparatusof FIG. 15 may perform S1400 of FIG. 14; the predictor of the decodingapparatus of FIG. 15 may perform S1410 to S1420 of FIG. 14; the residualprocessor of the decoding apparatus of FIG. 15 may perform S1430 toS1440 of FIG. 14; and the adder of the decoding apparatus of FIG. 15 mayperform S1450 of FIG. 14.

According to the aforementioned present disclosure, efficiency ofresidual coding can be improved.

In addition, according to the present disclosure, it is possible toimprove overall image/video compression efficiency and reduce the codingcomplexity by deriving the residual coefficients to which the simplifiedresidual data coding is applied without performing level mapping.

In addition, according to the present disclosure, the residualcoefficient to which the simplified residual data coding is applied mayhave a low correlation with the neighboring residual coefficients, andthus the efficiency of level mapping performed based on the neighboringresidual coefficients may be low. Accordingly, it is possible to reducecoding complexity and improve overall residual coding efficiency withoutperforming level mapping on the residual coefficients to which thesimplified residual data coding is applied.

In the above-described embodiment, the methods are described based onthe flowchart having a series of steps or blocks. The present disclosureis not limited to the order of the above steps or blocks. Some steps orblocks may occur simultaneously or in a different order from other stepsor blocks as described above. Further, those skilled in the art willunderstand that the steps shown in the above flowchart are notexclusive, that further steps may be included, or that one or more stepsin the flowchart may be deleted without affecting the scope of thepresent disclosure.

The embodiments described in this specification may be performed bybeing implemented on a processor, a microprocessor, a controller or achip. For example, the functional units shown in each drawing may beperformed by being implemented on a computer, a processor, amicroprocessor, a controller or a chip. In this case, information forimplementation (e.g., information on instructions) or algorithm may bestored in a digital storage medium.

In addition, the decoding apparatus and the encoding apparatus to whichthe present disclosure is applied may be included in a multimediabroadcasting transmission/reception apparatus, a mobile communicationterminal, a home cinema video apparatus, a digital cinema videoapparatus, a surveillance camera, a video chatting apparatus, areal-time communication apparatus such as video communication, a mobilestreaming apparatus, a storage medium, a camcorder, a VoD serviceproviding apparatus, an Over the top (OTT) video apparatus, an Internetstreaming service providing apparatus, a three-dimensional (3D) videoapparatus, a teleconference video apparatus, a transportation userequipment (e.g., vehicle user equipment, an airplane user equipment, aship user equipment, etc.) and a medical video apparatus and may be usedto process video signals and data signals. For example, the Over the top(OTT) video apparatus may include a game console, a blue-ray player, aninternet access TV, a home theater system, a smart phone, a tablet PC, aDigital Video Recorder (DVR), and the like.

Furthermore, the processing method to which the present disclosure isapplied may be produced in the form of a program that is to be executedby a computer and may be stored in a computer-readable recording medium.Multimedia data having a data structure according to the presentdisclosure may also be stored in computer-readable recording media. Thecomputer-readable recording media include all types of storage devicesin which data readable by a computer system is stored. Thecomputer-readable recording media may include a BD, a Universal SerialBus (USB), ROM, PROM, EPROM, EEPROM, RAM, CD-ROM, a magnetic tape, afloppy disk, and an optical data storage device, for example.Furthermore, the computer-readable recording media includes mediaimplemented in the form of carrier waves (e.g., transmission through theInternet). In addition, a bit stream generated by the encoding methodmay be stored in a computer-readable recording medium or may betransmitted over wired/wireless communication networks.

In addition, the embodiments of the present disclosure may beimplemented with a computer program product according to program codes,and the program codes may be performed in a computer by the embodimentsof the present disclosure. The program codes may be stored on a carrierwhich is readable by a computer.

FIG. 16 illustrates a structural diagram of a contents streaming systemto which the present disclosure is applied.

The content streaming system to which the embodiment(s) of the presentdisclosure is applied may largely include an encoding server, astreaming server, a web server, a media storage, a user device, and amultimedia input device.

The encoding server compresses content input from multimedia inputdevices such as a smartphone, a camera, a camcorder, etc. Into digitaldata to generate a bitstream and transmit the bitstream to the streamingserver. As another example, when the multimedia input devices such assmartphones, cameras, camcorders, etc. directly generate a bitstream,the encoding server may be omitted.

The bitstream may be generated by an encoding method or a bitstreamgenerating method to which the embodiment(s) of the present disclosureis applied, and the streaming server may temporarily store the bitstreamin the process of transmitting or receiving the bitstream.

The streaming server transmits the multimedia data to the user devicebased on a user's request through the web server, and the web serverserves as a medium for informing the user of a service. When the userrequests a desired service from the web server, the web server deliversit to a streaming server, and the streaming server transmits multimediadata to the user. In this case, the content streaming system may includea separate control server. In this case, the control server serves tocontrol a command/response between devices in the content streamingsystem.

The streaming server may receive content from a media storage and/or anencoding server. For example, when the content is received from theencoding server, the content may be received in real time. In this case,in order to provide a smooth streaming service, the streaming server maystore the bitstream for a predetermined time.

Examples of the user device may include a mobile phone, a smartphone, alaptop computer, a digital broadcasting terminal, a personal digitalassistant (PDA), a portable multimedia player (PMP), navigation, a slatePC, tablet PCs, ultrabooks, wearable devices (ex. Smartwatches, smartglasses, head mounted displays), digital TVs, desktops computer, digitalsignage, and the like. Each server in the content streaming system maybe operated as a distributed server, in which case data received fromeach server may be distributed.

The claims described in the present disclosure may be combined invarious ways. For example, the technical features of the method claimsof the present disclosure may be combined to be implemented as anapparatus, and the technical features of the apparatus claims of thepresent disclosure may be combined to be implemented as a method. Inaddition, the technical features of the method claim of the presentdisclosure and the technical features of the apparatus claim may becombined to be implemented as an apparatus, and the technical featuresof the method claim of the present disclosure and the technical featuresof the apparatus claim may be combined to be implemented as a method.

1. An image decoding method performed by a decoding apparatus, themethod comprising: obtaining image information including prediction modeinformation and residual information through a bitstream; deriving aprediction mode of a current block based on the prediction modeinformation; deriving a prediction sample based on the prediction mode;deriving a current residual coefficient based on residual syntaxelements for the current residual coefficient in the current block;deriving a residual sample based on the current residual coefficient;and deriving a reconstructed sample of the current block based on theresidual sample and the prediction sample, wherein the residualinformation includes the residual syntax elements for the currentresidual coefficient, wherein a number of context coded residual syntaxelements for residual coefficients prior to the current residualcoefficient among residual coefficients of the current block is equal toa maximum number of context coded bins of the current block, wherein theresidual syntax elements for the current residual coefficient includecoefficient level information for the current residual coefficient and asign flag of the current residual coefficient, and wherein an absolutelevel of the current residual coefficient is derived as a valueindicated by the coefficient level information for the current residualcoefficient, and a sign of the current residual coefficient is derivedas a sign indicated by the sign flag.
 2. The image decoding method ofclaim 1, wherein the current residual coefficient is derived withoutperforming level mapping.
 3. The image decoding method of claim 2,wherein the residual coefficients prior to the current residualcoefficient are derived by performing the level mapping.
 4. The imagedecoding method of claim 1, wherein the current block is a transformskip block.
 5. The image decoding method of claim 4, wherein the imageinformation includes a transform skip flag representing whethertransform is applied to the current block, and wherein a value of thetransform skip flag for the current block is
 1. 6. The image decodingmethod of claim 1, wherein the maximum number of the context coded binsof the current block is derived based on a width and a height of thecurrent block.
 7. The image decoding method of claim 1, wherein thecontext coded bins for the current block are all used as bins of thecontext coded residual syntax elements for the residual coefficientsprior to the current residual coefficient.
 8. The image decoding methodof claim 1, wherein the context-coded residual syntax elements include asignificant coefficient flag representing whether a residual coefficientis a non-zero residual coefficient, a parity level flag for a parity ofa coefficient level for the residual coefficient, a sign flagrepresenting a sign for the residual coefficient, a first coefficientlevel flag for whether the coefficient level is greater than a firstthreshold and a second coefficient level flag for whether thecoefficient level is greater than a second threshold.
 9. An imageencoding method performed by an encoding apparatus, the methodcomprising: deriving a prediction sample of a current block based oninter prediction or intra prediction; deriving a residual sample of thecurrent block based on the prediction sample; deriving a currentresidual coefficient based on the residual sample; and encoding imageinformation including prediction mode information representing aprediction mode of the current block and residual syntax elements forthe current residual coefficient, wherein a number of context codedresidual syntax elements for residual coefficients prior to the currentresidual coefficient among residual coefficients of the current block isequal to a maximum number of context coded bins of the current block,wherein the residual syntax elements for the current residualcoefficient include coefficient level information for the currentresidual coefficient and a sign flag of the current residualcoefficient, and wherein the coefficient level information represents anabsolute value of a coefficient level of the current residualcoefficient, and the sign flag of the current residual coefficientrepresents a sign of the current residual coefficient.
 10. The imageencoding method of claim 9, wherein the current block is a transformskip block.
 11. The image encoding method of claim 10, wherein the imageinformation includes a transform skip flag representing whethertransform is applied to the current block, and wherein a value of thetransform skip flag for the current block is
 1. 12. The image encodingmethod of claim 9, wherein the maximum number of the context coded binsof the current block is derived based on a width and a height of thecurrent block.
 13. The image encoding method of claim 9, wherein thecontext coded bins for the current block are all used as bins of thecontext coded residual syntax elements for the residual coefficientsprior to the current residual coefficient.
 14. The image encoding methodof claim 9, wherein the context-coded residual syntax elements include asignificant coefficient flag representing whether a residual coefficientis a non-zero residual coefficient, a parity level flag for a parity ofa coefficient level for the residual coefficient, a sign flagrepresenting a sign for the residual coefficient, a first coefficientlevel flag for whether the coefficient level is greater than a firstthreshold and a second coefficient level flag for whether thecoefficient level is greater than a second threshold.
 15. Anon-transitory computer-readable storage medium storing a bitstreamgenerated by a method, the method comprising: deriving a predictionsample of a current block based on inter prediction or intra prediction;deriving a residual sample of the current block based on the predictionsample; deriving a current residual coefficient based on the residualsample; encoding image information including prediction mode informationrepresenting a prediction mode of the current block and residual syntaxelements for the current residual coefficient; and generating thebitstream including the image information, wherein a number of contextcoded residual syntax elements for residual coefficients prior to thecurrent residual coefficient among residual coefficients of the currentblock is equal to a maximum number of context coded bins of the currentblock, wherein the residual syntax elements for the current residualcoefficient include coefficient level information for the currentresidual coefficient and a sign flag of the current residualcoefficient, and wherein the coefficient level information represents anabsolute value of a coefficient level of the current residualcoefficient, and the sign flag of the current residual coefficientrepresents a sign of the current residual coefficient.
 16. Atransmission method of data for image, the method comprising: obtaininga bitstream of image information including prediction mode informationrepresenting a prediction mode of a current block and residual syntaxelements for a current residual coefficient in the current block; andtransmitting the data including the bitstream of the image informationincluding the prediction mode information and the residual syntaxelements, wherein a prediction sample of the current block is derivedbased on inter prediction or intra prediction, and the prediction modeinformation is information whether the inter prediction or the intraprediction is applied to the current block as the prediction mode of thecurrent block, wherein the current residual coefficient is derived basedon a residual sample of the current block and the residual sample isderived based on the prediction sample of the current block, wherein anumber of context coded residual syntax elements for residualcoefficients prior to the current residual coefficient among residualcoefficients of the current block is equal to a maximum number ofcontext coded bins of the current block, wherein the residual syntaxelements for the current residual coefficient include coefficient levelinformation for the current residual coefficient and a sign flag of thecurrent residual coefficient, and wherein the coefficient levelinformation represents an absolute value of a coefficient level of thecurrent residual coefficient, and the sign flag of the current residualcoefficient represents a sign of the current residual coefficient.